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Overview
Comment: | Finish splitting the lang.in source file into separate parts. |
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Timelines: | family | ancestors | descendants | both | trunk |
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ca272c33f230ead0783f505e86cb3ed4 |
User & Date: | drh 2020-02-10 20:33:26.054 |
Context
2020-02-10
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20:43 | Improvements to the built-in function lists. (check-in: 8ff2f2f334 user: drh tags: trunk) | |
20:33 | Finish splitting the lang.in source file into separate parts. (check-in: ca272c33f2 user: drh tags: trunk) | |
17:23 | Work toward splitting up the "lang.in" source file into individual source files, one for each language topic. (check-in: 90730870c5 user: drh tags: trunk) | |
Changes
Changes to pages/lang.in.
︙ | ︙ | |||
63 64 65 66 67 68 69 70 71 72 73 74 75 76 77 78 79 80 81 82 83 84 | foreach {s_title s_tag s_kw} $section {} if {$s_kw == ""} { set s_kw $s_title } lappend lx [list $s_kw $s_title 0] } hd_list_of_links {} 340 $lx </tcl> </ul></td></tr></table> <p>^The routines [sqlite3_prepare_v2()], [sqlite3_prepare()], [sqlite3_prepare16()], [sqlite3_prepare16_v2()], [sqlite3_exec()], and [sqlite3_get_table()] accept an SQL statement list (sql-stmt-list) which is a semicolon-separated list of statements.</p> <tcl>BubbleDiagram sql-stmt-list</tcl> <p>Each SQL statement in the statement list is an instance of the following:</p> <tcl>BubbleDiagram sql-stmt</tcl> | > > > > > > < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < < | 63 64 65 66 67 68 69 70 71 72 73 74 75 76 77 78 79 80 81 82 83 84 85 86 87 88 89 90 | foreach {s_title s_tag s_kw} $section {} if {$s_kw == ""} { set s_kw $s_title } lappend lx [list $s_kw $s_title 0] } hd_list_of_links {} 340 $lx proc Operator {name} { return "<font color=\"#2c2cf0\"><big>$name</big></font>" } proc Example {text} { hd_puts "<blockquote><pre>$text</pre></blockquote>" } </tcl> </ul></td></tr></table> <p>^The routines [sqlite3_prepare_v2()], [sqlite3_prepare()], [sqlite3_prepare16()], [sqlite3_prepare16_v2()], [sqlite3_exec()], and [sqlite3_get_table()] accept an SQL statement list (sql-stmt-list) which is a semicolon-separated list of statements.</p> <tcl>BubbleDiagram sql-stmt-list</tcl> <p>Each SQL statement in the statement list is an instance of the following:</p> <tcl>BubbleDiagram sql-stmt</tcl> |
Added pages/lang_aggfunc.in.
> > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > | 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60 61 62 63 64 65 66 67 68 69 70 71 72 73 74 75 76 77 78 79 80 81 82 83 84 85 86 87 88 89 90 91 92 93 94 95 96 97 98 99 100 101 102 103 104 105 106 107 108 109 110 111 112 113 114 115 116 117 118 119 120 121 122 123 124 125 126 127 128 129 130 131 132 133 134 135 136 137 138 139 140 141 142 143 144 145 146 | <title>Built-in Aggregate Functions</title> <tcl> hd_keywords *aggfunc {Aggregate Functions} unset -nocomplain corefuncset proc funcdef {syntax keywords desc} { global corefuncset regexp {^[a-z_]+} $syntax basesyntax set corefuncset($basesyntax) [list $syntax $keywords $desc] } funcdef {avg(X)} {*avg {avg() aggregate function}} { ^The avg() function returns the average value of all non-NULL <i>X</i> within a group. ^String and BLOB values that do not look like numbers are interpreted as 0. ^The result of avg() is always a floating point value as long as at there is at least one non-NULL input even if all inputs are integers. ^The result of avg() is NULL if and only if there are no non-NULL inputs. } funcdef {count(X) count(*)} {*count {count() aggregate function}} { ^The count(X) function returns a count of the number of times that <i>X</i> is not NULL in a group. ^The count(*) function (with no arguments) returns the total number of rows in the group. } funcdef {group_concat(X) group_concat(X,Y)} { *group_concat {group_concat() aggregate function} } { ^The group_concat() function returns a string which is the concatenation of all non-NULL values of <i>X</i>. ^If parameter <i>Y</i> is present then it is used as the separator between instances of <i>X</i>. ^A comma (",") is used as the separator if <i>Y</i> is omitted. The order of the concatenated elements is arbitrary. } funcdef {max(X)} {*maxAggFunc *agg_max {max() aggregate function}} { ^The max() aggregate function returns the maximum value of all values in the group. ^The maximum value is the value that would be returned last in an ORDER BY on the same column. ^Aggregate max() returns NULL if and only if there are no non-NULL values in the group. } funcdef {min(X)} {*minAggFunc *agg_min {min() aggregate function}} { ^The min() aggregate function returns the minimum non-NULL value of all values in the group. ^The minimum value is the first non-NULL value that would appear in an ORDER BY of the column. ^Aggregate min() returns NULL if and only if there are no non-NULL values in the group. } funcdef {sum(X) total(X)} { *sumFunc *sum *total {sum() aggregate function} {total() aggregate function} } { ^The sum() and total() aggregate functions return sum of all non-NULL values in the group. ^If there are no non-NULL input rows then sum() returns NULL but total() returns 0.0. NULL is not normally a helpful result for the sum of no rows but the SQL standard requires it and most other SQL database engines implement sum() that way so SQLite does it in the same way in order to be compatible. The non-standard total() function is provided as a convenient way to work around this design problem in the SQL language.</p> <p>^The result of total() is always a floating point value. ^The result of sum() is an integer value if all non-NULL inputs are integers. ^If any input to sum() is neither an integer or a NULL then sum() returns a floating point value which might be an approximation to the true sum.</p> <p>^Sum() will throw an "integer overflow" exception if all inputs are integers or NULL and an integer overflow occurs at any point during the computation. ^Total() never throws an integer overflow. } </tcl> <fancy_format> <tcl> RecursiveBubbleDiagram aggregate-function-invocation </tcl> <p> The aggregate functions shown below are available by default. Additional aggregate functions written in C may be added using the [sqlite3_create_function()]</a> API.</p> <p> ^In any aggregate function that takes a single argument, that argument can be preceded by the keyword DISTINCT. ^In such cases, duplicate elements are filtered before being passed into the aggregate function. ^For example, the function "count(distinct X)" will return the number of distinct values of column X instead of the total number of non-null values in column X. </p> <tcl>hd_fragment aggfilter {FILTER clause on aggregate functions}</tcl> <p> If a FILTER clause is provided, then only rows for which the <i>expr</i> is true are included in the aggregate. </p> <tcl> set lx {} foreach basesyntax [array names corefuncset] { foreach {syntax keywords desc} $corefuncset($basesyntax) break regexp {^[a-z_]+} $basesyntax fragment foreach coresyntax $syntax { lappend lx [list $fragment $coresyntax 0] } } hd_list_of_links {} 225 [lsort -index 1 $lx] hd_putsnl "<hr class='xhr'>" hd_putsnl "<dl>" foreach basesyntax [lsort [array names corefuncset]] { foreach {syntax keywords desc} $corefuncset($basesyntax) break regsub -all {\s+} [string trim $syntax] {<br />} syntax regsub -all {\(([^*)]+)\)} $syntax {(<i>\1</i>)} syntax regsub -all {,} $syntax {</i>,<i>} syntax regsub -all {<i>\.\.\.</i>} $syntax {...} syntax regexp {^[a-z]+} $basesyntax fragment if {[llength $keywords]==0} { regexp {[a-z_]+} $syntax name hd_fragment $name *$name "${name}() SQL function" } else { set fragname [lindex $keywords 0] regsub -all {[^a-z]} $fragname {} fragname hd_fragment $fragname eval hd_keywords [string map {\n { }} $keywords] } hd_puts "<dt><p><b>$syntax</b></dt>" hd_resolve "<dd><p>$desc</dd>\n" } hd_putsnl "</dl>" |
Added pages/lang_conflict.in.
> > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > | 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60 61 62 63 64 65 66 67 68 69 70 71 72 73 74 75 76 77 78 79 80 81 82 83 84 85 86 87 88 89 90 91 92 93 94 95 96 97 98 99 100 101 102 103 104 105 106 107 108 109 110 111 112 113 114 115 | <title>The ON CONFLICT Clause</title> <tcl> hd_keywords *conflict {conflict clause} {ON CONFLICT} {ON CONFLICT clause} </tcl> <fancy_format> <tcl> RecursiveBubbleDiagram conflict-clause </tcl> <p>The ON CONFLICT clause is a non-standard extension specific to SQLite that can appear in many other SQL commands. It is given its own section in this document because it is not part of standard SQL and therefore might not be familiar.</p> <p>The ON CONFLICT clause described here has been a part of SQLite since before version 3.0.0 ([dateof:3.0.0]). The phrase "ON CONFLICT" is also part of [UPSERT], which is an extension to [INSERT] added in version 3.24.0 ([dateof:3.24.0]). Do not confuse these two separate uses of the "ON CONFLICT" phrase. <p>^The syntax for the ON CONFLICT clause is as shown above for the CREATE TABLE command. ^For the INSERT and UPDATE commands, the keywords "ON CONFLICT" are replaced by "OR" so that the syntax reads more naturally. For example, instead of "INSERT ON CONFLICT IGNORE" we have "INSERT OR IGNORE". The keywords change but the meaning of the clause is the same either way.</p> <p>The ON CONFLICT clause applies to [UNIQUE], [NOT NULL], [CHECK], and [PRIMARY KEY] constraints. The ON CONFLICT algorithm does not apply to [FOREIGN KEY constraints]. There are five conflict resolution algorithm choices: ROLLBACK, ABORT, FAIL, IGNORE, and REPLACE. ^The default conflict resolution algorithm is ABORT. This is what they mean:</p> <dl> <dt><b>ROLLBACK</b></dt> <dd><p> ^When an applicable constraint violation occurs, the ROLLBACK resolution algorithm aborts the current SQL statement with an SQLITE_CONSTRAINT error and rolls back the current transaction. ^If no transaction is active (other than the implied transaction that is created on every command) then the ROLLBACK resolution algorithm works the same as the ABORT algorithm.</p></dd> <dt><b>ABORT</b></dt> <dd><p> ^When an applicable constraint violation occurs, the ABORT resolution algorithm aborts the current SQL statement with an SQLITE_CONSTRAINT error and backs out any changes made by the current SQL statement; but changes caused by prior SQL statements within the same transaction are preserved and the transaction remains active. This is the default behavior and the behavior specified by the SQL standard.</p></dd> <dt><b>FAIL</b></dt> <dd><p> ^When an applicable constraint violation occurs, the FAIL resolution algorithm aborts the current SQL statement with an SQLITE_CONSTRAINT error. ^But the FAIL resolution does not back out prior changes of the SQL statement that failed nor does it end the transaction. ^For example, if an UPDATE statement encountered a constraint violation on the 100th row that it attempts to update, then the first 99 row changes are preserved but changes to rows 100 and beyond never occur.</p> <p>The FAIL behavior only works for uniqueness, NOT NULL, and CHECK constraints. A [foreign key constraint] violation causes an ABORT. </p></dd> <dt><b>IGNORE</b></dt> <dd><p> ^When an applicable constraint violation occurs, the IGNORE resolution algorithm skips the one row that contains the constraint violation and continues processing subsequent rows of the SQL statement as if nothing went wrong. Other rows before and after the row that contained the constraint violation are inserted or updated normally. ^No error is returned for uniqueness, NOT NULL, and UNIQUE constraint errors when the IGNORE conflict resolution algorithm is used. ^However, the IGNORE conflict resolution algorithm works like ABORT for [foreign key constraint] errors. </p> </dd> <dt><b>REPLACE</b></dt> <dd><p> ^When a [UNIQUE] or [PRIMARY KEY] constraint violation occurs, the REPLACE algorithm deletes pre-existing rows that are causing the constraint violation prior to inserting or updating the current row and the command continues executing normally. ^If a [NOT NULL] constraint violation occurs, the REPLACE conflict resolution replaces the NULL value with the default value for that column, or if the column has no default value, then the ABORT algorithm is used. ^If a [CHECK constraint] or [foreign key constraint] violation occurs, the REPLACE conflict resolution algorithm works like ABORT.</p> <p>^When the REPLACE conflict resolution strategy deletes rows in order to satisfy a constraint, [CREATE TRIGGER | delete triggers] fire if and only if [recursive_triggers pragma | recursive triggers] are enabled.</p> <p>^The [sqlite3_update_hook | update hook] is not invoked for rows that are deleted by the REPLACE conflict resolution strategy. ^Nor does REPLACE increment the [sqlite3_changes | change counter]. The exceptional behaviors defined in this paragraph might change in a future release.</p> </dl> <p>^The algorithm specified in the OR clause of an INSERT or UPDATE overrides any algorithm specified in a CREATE TABLE. ^If no algorithm is specified anywhere, the ABORT algorithm is used.</p> |
Added pages/lang_corefunc.in.
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Note that the X and Y arguments are reversed in the glob() function relative to the infix [GLOB] operator. Y is the string and X is the pattern. So, for example, the following expressions are equivalent: <blockquote><pre> name GLOB '*helium*' glob('*helium*',name) </pre></blockquote> <p>^If the [sqlite3_create_function()] interface is used to override the glob(X,Y) function with an alternative implementation then the [GLOB] operator will invoke the alternative implementation. } funcdef {ifnull(X,Y)} {} { ^The ifnull() function returns a copy of its first non-NULL argument, or NULL if both arguments are NULL. ^Ifnull() must have exactly 2 arguments. ^The ifnull() function is equivalent to [coalesce()] with two arguments. } funcdef {instr(X,Y)} {} { ^The instr(X,Y) function finds the first occurrence of string Y within string X and returns the number of prior characters plus 1, or 0 if Y is nowhere found within X. ^Or, if X and Y are both BLOBs, then instr(X,Y) returns one more than the number bytes prior to the first occurrence of Y, or 0 if Y does not occur anywhere within X. ^If both arguments X and Y to instr(X,Y) are non-NULL and are not BLOBs then both are interpreted as strings. ^If either X or Y are NULL in instr(X,Y) then the result is NULL. } funcdef {hex(X)} {} { ^The hex() function interprets its argument as a BLOB and returns a string which is the upper-case hexadecimal rendering of the content of that blob. } funcdef {last_insert_rowid()} {} { ^The last_insert_rowid() function returns the [ROWID] of the last row insert from the database connection which invoked the function. ^The last_insert_rowid() SQL function is a wrapper around the [sqlite3_last_insert_rowid()] C/C++ interface function. } funcdef {length(X)} {} { ^For a string value X, the length(X) function returns the number of characters (not bytes) in X prior to the first NUL character. Since SQLite strings do not normally contain NUL characters, the length(X) function will usually return the total number of characters in the string X. ^For a blob value X, length(X) returns the number of bytes in the blob. ^If X is NULL then length(X) is NULL. ^If X is numeric then length(X) returns the length of a string representation of X. } funcdef {like(X,Y) like(X,Y,Z)} {} { ^The like() function is used to implement the "<b>Y LIKE X [ESCAPE Z]</b>" expression. ^If the optional ESCAPE clause is present, then the like() function is invoked with three arguments. ^Otherwise, it is invoked with two arguments only. Note that the X and Y parameters are reversed in the like() function relative to the infix [LIKE] operator. X is the pattern and Y is the string to match against that pattern. Hence, the following expressions are equivalent: <blockquote><pre> name LIKE '%neon%' like('%neon%',name) </pre></blockquote> ^The [sqlite3_create_function()] interface can be used to override the like() function and thereby change the operation of the [LIKE] operator. When overriding the like() function, it may be important to override both the two and three argument versions of the like() function. Otherwise, different code may be called to implement the [LIKE] operator depending on whether or not an ESCAPE clause was specified. } funcdef {likelihood(X,Y)} {} { ^The likelihood(X,Y) function returns argument X unchanged. ^(The value Y in likelihood(X,Y) must be a floating point constant between 0.0 and 1.0, inclusive.)^ ^The likelihood(X) function is a no-op that the code generator optimizes away so that it consumes no CPU cycles during run-time (that is, during calls to [sqlite3_step()]). ^The purpose of the likelihood(X,Y) function is to provide a hint to the query planner that the argument X is a boolean that is true with a probability of approximately Y. ^(The [unlikely(X)] function is short-hand for likelihood(X,0.0625).)^ ^(The [likely(X)] function is short-hand for likelihood(X,0.9375).)^ } funcdef {likely(X)} {} { ^The likely(X) function returns the argument X unchanged. ^The likely(X) function is a no-op that the code generator optimizes away so that it consumes no CPU cycles at run-time (that is, during calls to [sqlite3_step()]). ^The purpose of the likely(X) function is to provide a hint to the query planner that the argument X is a boolean value that is usually true. ^(The likely(X) function is equivalent to [likelihood](X,0.9375).)^ See also: [unlikely(X)]. } funcdef {load_extension(X) load_extension(X,Y)} {} { ^The load_extension(X,Y) function loads [SQLite extensions] out of the shared library file named X using the entry point Y. ^The result of load_extension() is always a NULL. ^If Y is omitted then the default entry point name is used. ^The load_extension() function raises an exception if the extension fails to load or initialize correctly. <p>^The load_extension() function will fail if the extension attempts to modify or delete an SQL function or collating sequence. ^The extension can add new functions or collating sequences, but cannot modify or delete existing functions or collating sequences because those functions and/or collating sequences might be used elsewhere in the currently running SQL statement. To load an extension that changes or deletes functions or collating sequences, use the [sqlite3_load_extension()] C-language API.</p> <p>For security reasons, extension loaded is turned off by default and must be enabled by a prior call to [sqlite3_enable_load_extension()].</p> } funcdef {lower(X)} {} { ^The lower(X) function returns a copy of string X with all ASCII characters converted to lower case. ^The default built-in lower() function works for ASCII characters only. To do case conversions on non-ASCII characters, load the ICU extension. } funcdef {ltrim(X) ltrim(X,Y)} {} { ^The ltrim(X,Y) function returns a string formed by removing any and all characters that appear in Y from the left side of X. ^If the Y argument is omitted, ltrim(X) removes spaces from the left side of X. } funcdef {max(X,Y,...)} {*maxCoreFunc *max {max() SQL function}} { ^The multi-argument max() function returns the argument with the maximum value, or return NULL if any argument is NULL. ^The multi-argument max() function searches its arguments from left to right for an argument that defines a collating function and uses that collating function for all string comparisons. ^If none of the arguments to max() define a collating function, then the BINARY collating function is used. ^(Note that <b>max()</b> is a simple function when it has 2 or more arguments but operates as an [maxAggFunc | aggregate function] if given only a single argument.)^ } funcdef {min(X,Y,...)} {*minCoreFunc *min {min() SQL function}} { ^The multi-argument min() function returns the argument with the minimum value. ^The multi-argument min() function searches its arguments from left to right for an argument that defines a collating function and uses that collating function for all string comparisons. ^If none of the arguments to min() define a collating function, then the BINARY collating function is used. ^(Note that <b>min()</b> is a simple function when it has 2 or more arguments but operates as an [minAggFunc | aggregate function] if given only a single argument.)^ } funcdef {nullif(X,Y)} {} { ^The nullif(X,Y) function returns its first argument if the arguments are different and NULL if the arguments are the same. ^The nullif(X,Y) function searches its arguments from left to right for an argument that defines a collating function and uses that collating function for all string comparisons. ^If neither argument to nullif() defines a collating function then the BINARY is used. } funcdef {printf(FORMAT,...)} {} { ^(The printf(FORMAT,...) SQL function works like the [sqlite3_mprintf()] C-language function and the printf() function from the standard C library.)^ The first argument is a format string that specifies how to construct the output string using values taken from subsequent arguments. ^If the FORMAT argument is missing or NULL then the result is NULL. ^The %n format is silently ignored and does not consume an argument. ^The %p format is an alias for %X. ^The %z format is interchangeable with %s. ^(If there are too few arguments in the argument list, missing arguments are assumed to have a NULL value, which is translated into 0 or 0.0 for numeric formats or an empty string for %s.)^ See the [built-in printf()] documentation for additional information. } funcdef {quote(X)} {} { ^The quote(X) function returns the text of an SQL literal which is the value of its argument suitable for inclusion into an SQL statement. ^Strings are surrounded by single-quotes with escapes on interior quotes as needed. ^BLOBs are encoded as hexadecimal literals. ^Strings with embedded NUL characters cannot be represented as string literals in SQL and hence the returned string literal is truncated prior to the first NUL. } funcdef {random()} {} { ^The random() function returns a pseudo-random integer between -9223372036854775808 and +9223372036854775807. } funcdef {randomblob(N)} {} { ^The randomblob(N) function return an N-byte blob containing pseudo-random bytes. ^If N is less than 1 then a 1-byte random blob is returned. <p>Hint: applications can generate globally unique identifiers using this function together with [hex()] and/or [lower()] like this:</p> <blockquote> hex(randomblob(16))<br></br> lower(hex(randomblob(16))) </blockquote> } funcdef {replace(X,Y,Z)} {} { ^The replace(X,Y,Z) function returns a string formed by substituting string Z for every occurrence of string Y in string X. ^The [BINARY] collating sequence is used for comparisons. ^If Y is an empty string then return X unchanged. ^If Z is not initially a string, it is cast to a UTF-8 string prior to processing. } funcdef {round(X) round(X,Y)} {} { ^The round(X,Y) function returns a floating-point value X rounded to Y digits to the right of the decimal point. ^If the Y argument is omitted, it is assumed to be 0. } funcdef {rtrim(X) rtrim(X,Y)} {} { ^The rtrim(X,Y) function returns a string formed by removing any and all characters that appear in Y from the right side of X. ^If the Y argument is omitted, rtrim(X) removes spaces from the right side of X. } funcdef {soundex(X)} {} { ^The soundex(X) function returns a string that is the soundex encoding of the string X. ^The string "?000" is returned if the argument is NULL or contains no ASCII alphabetic characters. ^(This function is omitted from SQLite by default. It is only available if the [SQLITE_SOUNDEX] compile-time option is used when SQLite is built.)^ } funcdef {sqlite_compileoption_get(N)} {} { ^The sqlite_compileoption_get() SQL function is a wrapper around the [sqlite3_compileoption_get()] C/C++ function. ^This routine returns the N-th compile-time option used to build SQLite or NULL if N is out of range. See also the [compile_options pragma]. } funcdef {sqlite_compileoption_used(X)} {} { ^The sqlite_compileoption_used() SQL function is a wrapper around the [sqlite3_compileoption_used()] C/C++ function. ^When the argument X to sqlite_compileoption_used(X) is a string which is the name of a compile-time option, this routine returns true (1) or false (0) depending on whether or not that option was used during the build. } funcdef {sqlite_offset(X)} {} { ^The sqlite_offset(X) function returns the byte offset in the database file for the beginning of the record from which value would be read. If X is not a column in an ordinary table, then sqlite_offset(X) returns NULL. The value returned by sqlite_offset(X) might reference either the original table or an index, depending on the query. If the value X would normally be extracted from an index, the sqlite_offset(X) returns the offset to the corresponding index record. If the value X would be extracted from the original table, then sqlite_offset(X) returns the offset to the table record. <p>The sqlite_offset(X) SQL function is only available if SQLite is built using the [-DSQLITE_ENABLE_OFFSET_SQL_FUNC] compile-time option. } funcdef {sqlite_source_id()} {} { ^The sqlite_source_id() function returns a string that identifies the specific version of the source code that was used to build the SQLite library. ^The string returned by sqlite_source_id() is the date and time that the source code was checked in followed by the SHA1 hash for that check-in. ^This function is an SQL wrapper around the [sqlite3_sourceid()] C interface. } funcdef {sqlite_version()} {} { ^The sqlite_version() function returns the version string for the SQLite library that is running. ^This function is an SQL wrapper around the [sqlite3_libversion()] C-interface. } funcdef {substr(X,Y,Z) substr(X,Y)} {} { ^The substr(X,Y,Z) function returns a substring of input string X that begins with the Y-th character and which is Z characters long. ^If Z is omitted then substr(X,Y) returns all characters through the end of the string X beginning with the Y-th. ^The left-most character of X is number 1. ^If Y is negative then the first character of the substring is found by counting from the right rather than the left. ^If Z is negative then the abs(Z) characters preceding the Y-th character are returned. ^If X is a string then characters indices refer to actual UTF-8 characters. ^If X is a BLOB then the indices refer to bytes. } funcdef {total_changes()} {} { ^The total_changes() function returns the number of row changes caused by INSERT, UPDATE or DELETE statements since the current database connection was opened. ^This function is a wrapper around the [sqlite3_total_changes()] C/C++ interface. } funcdef {trim(X) trim(X,Y)} {} { ^The trim(X,Y) function returns a string formed by removing any and all characters that appear in Y from both ends of X. ^If the Y argument is omitted, trim(X) removes spaces from both ends of X. } funcdef {typeof(X)} {} { ^The typeof(X) function returns a string that indicates the [datatype] of the expression X: "null", "integer", "real", "text", or "blob". } funcdef {unlikely(X)} {} { ^The unlikely(X) function returns the argument X unchanged. ^The unlikely(X) function is a no-op that the code generator optimizes away so that it consumes no CPU cycles at run-time (that is, during calls to [sqlite3_step()]). ^The purpose of the unlikely(X) function is to provide a hint to the query planner that the argument X is a boolean value that is usually not true. ^(The unlikely(X) function is equivalent to [likelihood](X, 0.0625).)^ } funcdef {unicode(X)} {} { ^The unicode(X) function returns the numeric unicode code point corresponding to the first character of the string X. If the argument to unicode(X) is not a string then the result is undefined. } funcdef {upper(X)} {} { ^The upper(X) function returns a copy of input string X in which all lower-case ASCII characters are converted to their upper-case equivalent. } funcdef {zeroblob(N)} {} { ^The zeroblob(N) function returns a BLOB consisting of N bytes of 0x00. SQLite manages these zeroblobs very efficiently. Zeroblobs can be used to reserve space for a BLOB that is later written using [sqlite3_blob_open() | incremental BLOB I/O]. ^This SQL function is implemented using the [sqlite3_result_zeroblob()] routine from the C/C++ interface. } </tcl> <fancy_format> <p>The core functions shown below are available by default. [datefunc | Date & Time functions], [aggfunc | aggregate functions], [builtin window functions|window functions], and [json1 | JSON functions] are documented separately. An application may define additional functions written in C and added to the database engine using the [sqlite3_create_function()] API.</p> <tcl> set lx {} foreach basesyntax [array names corefuncset] { foreach {syntax keywords desc} $corefuncset($basesyntax) break regexp {^[a-z_]+} $basesyntax fragment foreach coresyntax $syntax { lappend lx [list $fragment $coresyntax 0] } } hd_putsnl "<p>" hd_list_of_links {} 300 [lsort -index 1 $lx] hd_putsnl "<hr class='xhr'>" hd_putsnl "<dl>" foreach basesyntax [lsort [array names corefuncset]] { foreach {syntax keywords desc} $corefuncset($basesyntax) break regsub -all {\s+} [string trim $syntax] {<br />} syntax regsub -all {\(([^*)]+)\)} $syntax {(<i>\1</i>)} syntax regsub -all {,} $syntax {</i>,<i>} syntax regsub -all {<i>\.\.\.</i>} $syntax {...} syntax regexp {^[a-z]+} $basesyntax fragment if {[llength $keywords]==0} { regexp {[a-z_]+} $syntax name hd_fragment $name *$name "${name}() SQL function" } else { set fragname [lindex $keywords 0] regsub -all {[^a-z]} $fragname {} fragname hd_fragment $fragname eval hd_keywords [string map {\n { }} $keywords] } hd_puts "<dt><p><b>$syntax</b></dt>" hd_resolve "<dd><p>$desc</dd>\n" } hd_putsnl "</dl>" |
Added pages/lang_createtrigger.in.
> > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > | 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60 61 62 63 64 65 66 67 68 69 70 71 72 73 74 75 76 77 78 79 80 81 82 83 84 85 86 87 88 89 90 91 92 93 94 95 96 97 98 99 100 101 102 103 104 105 106 107 108 109 110 111 112 113 114 115 116 117 118 119 120 121 122 123 124 125 126 127 128 129 130 131 132 133 134 135 136 137 138 139 140 141 142 143 144 145 146 147 148 149 150 151 152 153 154 155 156 157 158 159 160 161 162 163 164 165 166 167 168 169 170 171 172 173 174 175 176 177 178 179 180 181 182 183 184 185 186 187 188 189 190 191 192 193 194 195 196 197 198 199 200 201 202 203 204 205 206 207 208 209 210 211 212 213 214 215 216 217 218 219 220 221 222 223 224 225 226 227 228 229 230 231 232 233 234 235 236 237 238 239 240 241 242 243 244 245 246 247 248 249 250 251 252 253 254 255 256 257 258 259 260 261 262 263 264 265 266 267 268 269 270 271 | <title>CREATE TRIGGER</title> <tcl> hd_keywords *createtrigger {CREATE TRIGGER} </tcl> <table_of_contents> <h1>Syntax</h1> <tcl> RecursiveBubbleDiagram create-trigger-stmt </tcl> <h1>Description</h1> <p>^The CREATE TRIGGER statement is used to add triggers to the database schema. ^Triggers are database operations that are automatically performed when a specified database event occurs. </p> <p>^Each trigger must specify that it will fire for one of the following operations: [DELETE], [INSERT], [UPDATE]. The trigger fires once for each row that is deleted, inserted, or updated. If the "UPDATE OF <yyterm>column-name</yyterm>" syntax is used, then the trigger will only fire if <yyterm>column-name</yyterm> appears on the left-hand side of one of the terms in the SET clause of the [UPDATE] statement.</p> <p>Due to an historical oversight, columns named in the "UPDATE OF" clause do not actually have to exist in the table being updated. Unrecognized column names are silently ignored. It would be more helpful if SQLite would fail the CREATE TRIGGER statement if any of the names in the "UPDATE OF" clause are not columns in the table. However, as this problem was discovered many years after SQLite was widely deployed, we have resisted fixing the problem for fear of breaking legacy applications.</p> <p>^At this time SQLite supports only FOR EACH ROW triggers, not FOR EACH STATEMENT triggers. ^Hence explicitly specifying FOR EACH ROW is optional. ^FOR EACH ROW implies that the SQL statements specified in the trigger may be executed (depending on the WHEN clause) for each database row being inserted, updated or deleted by the statement causing the trigger to fire.</p> <p>^(Both the WHEN clause and the trigger actions may access elements of the row being inserted, deleted or updated using references of the form "NEW.<i>column-name</i>" and "OLD.<i>column-name</i>", where <i>column-name</i> is the name of a column from the table that the trigger is associated with.)^ ^(OLD and NEW references may only be used in triggers on events for which they are relevant, as follows:</p> <table border=0 cellpadding=10> <tr> <td valign="top" align="right" width=120><i>INSERT</i></td> <td valign="top">NEW references are valid</td> </tr> <tr> <td valign="top" align="right" width=120><i>UPDATE</i></td> <td valign="top">NEW and OLD references are valid</td> </tr> <tr> <td valign="top" align="right" width=120><i>DELETE</i></td> <td valign="top">OLD references are valid</td> </tr> </table> </p>)^ <p>^If a WHEN clause is supplied, the SQL statements specified are only executed if the WHEN clause is true. ^If no WHEN clause is supplied, the SQL statements are executed every time the trigger fires.</p> <p>^The BEFORE or AFTER keyword determines when the trigger actions will be executed relative to the insertion, modification or removal of the associated row.</p> <p>^An [ON CONFLICT] clause may be specified as part of an [UPDATE] or [INSERT] action within the body of the trigger. ^However if an [ON CONFLICT] clause is specified as part of the statement causing the trigger to fire, then conflict handling policy of the outer statement is used instead.</p> <p>^Triggers are automatically [DROP TRIGGER | dropped] when the table that they are associated with (the <i>table-name</i> table) is [DROP TABLE | dropped]. ^However if the trigger actions reference other tables, the trigger is not dropped or modified if those other tables are [DROP TABLE | dropped] or [ALTER TABLE | modified].</p> <p>^Triggers are removed using the [DROP TRIGGER] statement.</p> <h2>Syntax Restrictions On UPDATE, DELETE, and INSERT Statements Within Triggers</h2> <p>^The [UPDATE], [DELETE], and [INSERT] statements within triggers do not support the full syntax for [UPDATE], [DELETE], and [INSERT] statements. The following restrictions apply:</p> <ul> <li><p> ^(The name of the table to be modified in an [UPDATE], [DELETE], or [INSERT] statement must be an unqualified table name. In other words, one must use just "<i>tablename</i>" not "<i>database</i><b>.</b><i>tablename</i>" when specifying the table.)^ </p></li> <li><p> ^For non-TEMP triggers, the table to be modified or queried must exist in the same database as the table or view to which the trigger is attached. ^(TEMP triggers are not subject to the same-database rule. A TEMP trigger is allowed to query or modify any table in any [ATTACH]-ed database.)^ </p></li> <li><p> ^The "INSERT INTO <i>table</i> DEFAULT VALUES" form of the [INSERT] statement is not supported. </p></li> <li><p> ^The INDEXED BY and NOT INDEXED clauses are not supported for [UPDATE] and [DELETE] statements. </p></li> <li><p> ^(The ORDER BY and LIMIT clauses on [UPDATE] and [DELETE] statements are not supported. ORDER BY and LIMIT are not normally supported for [UPDATE] or [DELETE] in any context but can be enabled for top-level statements using the [SQLITE_ENABLE_UPDATE_DELETE_LIMIT] compile-time option. However, that compile-time option only applies to top-level [UPDATE] and [DELETE] statements, not [UPDATE] and [DELETE] statements within triggers.)^ </p></li> <li><p> ^[common-table-expression|Common table expression] are not supported for statements inside of triggers. </p></li> </ul> <tcl>hd_fragment instead_of_trigger {INSTEAD OF} {INSTEAD OF trigger}</tcl> <h1>INSTEAD OF triggers</h1> <p>^Triggers may be created on [views], as well as ordinary tables, by specifying INSTEAD OF in the CREATE TRIGGER statement. ^If one or more ON INSERT, ON DELETE or ON UPDATE triggers are defined on a view, then it is not an error to execute an INSERT, DELETE or UPDATE statement on the view, respectively. ^Instead, executing an INSERT, DELETE or UPDATE on the view causes the associated triggers to fire. ^The real tables underlying the view are not modified (except possibly explicitly, by a trigger program).</p> <p>^Note that the [sqlite3_changes()] and [sqlite3_total_changes()] interfaces do not count INSTEAD OF trigger firings, but the [count_changes pragma] does count INSTEAD OF trigger firing.</p> <h1>Some Example Triggers</h1> <p>^(Assuming that customer records are stored in the "customers" table, and that order records are stored in the "orders" table, the following UPDATE trigger ensures that all associated orders are redirected when a customer changes his or her address:</p> <tcl>Example { CREATE TRIGGER update_customer_address UPDATE OF address ON customers BEGIN UPDATE orders SET address = new.address WHERE customer_name = old.name; END; }</tcl> <p>With this trigger installed, executing the statement:</p> <tcl>Example { UPDATE customers SET address = '1 Main St.' WHERE name = 'Jack Jones'; }</tcl> <p>causes the following to be automatically executed:</p> <tcl>Example { UPDATE orders SET address = '1 Main St.' WHERE customer_name = 'Jack Jones'; }</tcl>)^ <p>For an example of an INSTEAD OF trigger, consider the following schema: <tcl>Example { CREATE TABLE customer( cust_id INTEGER PRIMARY KEY, cust_name TEXT, cust_addr TEXT ); CREATE VIEW customer_address AS SELECT cust_id, cust_addr FROM customer; CREATE TRIGGER cust_addr_chng INSTEAD OF UPDATE OF cust_addr ON customer_address BEGIN UPDATE customer SET cust_addr=NEW.cust_addr WHERE cust_id=NEW.cust_id; END; }</tcl> <p>With the schema above, a statement of the form:</p> <tcl>Example { UPDATE customer_address SET cust_addr=$new_address WHERE cust_id=$cust_id; }</tcl> <p>Causes the customer.cust_addr field to be updated for a specific customer entry that has customer.cust_id equal to the $cust_id parameter. Note how the values assigned to the view are made available as field in the special "NEW" table within the trigger body.</p> <tcl>hd_fragment undef_before {undefined BEFORE trigger behavior}</tcl> <h1>Cautions On The Use Of BEFORE triggers</h1> <p>If a BEFORE UPDATE or BEFORE DELETE trigger modifies or deletes a row that was to have been updated or deleted, then the result of the subsequent update or delete operation is undefined. Furthermore, if a BEFORE trigger modifies or deletes a row, then it is undefined whether or not AFTER triggers that would have otherwise run on those rows will in fact run. </p> <p>The value of NEW.rowid is undefined in a BEFORE INSERT trigger in which the rowid is not explicitly set to an integer.</p> <p>Because of the behaviors described above, programmers are encouraged to prefer AFTER triggers over BEFORE triggers.</p> <tcl>hd_fragment raise {RAISE function}</tcl> <h1>The RAISE() function</h1> <p>^(A special SQL function RAISE() may be used within a trigger-program,)^ with the following syntax</p> <tcl>BubbleDiagram raise-function</tcl> <p>^(When one of RAISE(ROLLBACK,...), RAISE(ABORT,...) or RAISE(FAIL,...) is called during trigger-program execution, the specified [ON CONFLICT] processing is performed the current query terminates.)^ An error code of [SQLITE_CONSTRAINT] is returned to the application, along with the specified error message.</p> <p>^When RAISE(IGNORE) is called, the remainder of the current trigger program, the statement that caused the trigger program to execute and any subsequent trigger programs that would have been executed are abandoned. ^No database changes are rolled back. ^If the statement that caused the trigger program to execute is itself part of a trigger program, then that trigger program resumes execution at the beginning of the next step. </p> <tcl>hd_fragment temptrig {TEMP triggers on non-TEMP tables}</tcl> <h1>TEMP Triggers on Non-TEMP Tables</h1> <p>^(A trigger normally exists in the same database as the table named after the "ON" keyword in the CREATE TRIGGER statement. Except, it is possible to create a TEMP TRIGGER on a table in another database.)^ Such a trigger will only fire when changes are made to the target table by the application that defined the trigger. Other applications that modify the database will not be able to see the TEMP trigger and hence cannot run the trigger.</p> <p>When defining a TEMP trigger on a non-TEMP table, it is important to specify the database holding the non-TEMP table. For example, in the following statement, it is important to say "main.tab1" instead of just "tab1":</p> <blockquote><pre> CREATE TEMP TRIGGER ex1 AFTER INSERT ON <b>main.</b>tab1 BEGIN ... </pre></blockquote> <p>Failure to specify the schema name on the target table could result in the TEMP trigger being reattached to a table with the same name in another database whenever any schema change occurs.</p> |
Added pages/lang_createview.in.
> > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > | 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 | <title>CREATE VIEW</title> <tcl> hd_keywords *createview {CREATE VIEW} view VIEW *views </tcl> <fancy_format> <h1>Syntax</h1> <tcl> RecursiveBubbleDiagram create-view-stmt </tcl> <h1>Description</h1> <p>^The CREATE VIEW command assigns a name to a pre-packaged [SELECT] statement. ^Once the view is created, it can be used in the FROM clause of another [SELECT] in place of a table name. </p> <p>^If the "TEMP" or "TEMPORARY" keyword occurs in between "CREATE" and "VIEW" then the view that is created is only visible to the [database connection] that created it and is automatically deleted when the database connection is closed.</p> <p> ^If a <yyterm>schema-name</yyterm> is specified, then the view is created in the specified database. ^It is an error to specify both a <yyterm>schema-name</yyterm> and the TEMP keyword on a VIEW, unless the <yyterm>schema-name</yyterm> is "temp". ^If no schema name is specified, and the TEMP keyword is not present, the VIEW is created in the main database.</p> <p>^You cannot [DELETE], [INSERT], or [UPDATE] a view. ^Views are read-only in SQLite. ^However, in many cases you can use an [INSTEAD OF trigger] on the view to accomplish the same thing. ^Views are removed with the [DROP VIEW] command.</p> <p>^If a <yyterm>column-name</yyterm> list follows the <yyterm>view-name</yyterm>, then that list determines the names of the columns for the view. ^If the <yyterm>column-name</yyterm> list is omitted, then the names of the columns in the view are derived from the names of the result-set columns in the [select-stmt]. The use of <yyterm>column-name</yyterm> list is recommended. Or, if <yyterm>column-name</yyterm> list is omitted, then the result columns in the [SELECT] statement that defines the view should have well-defined names using the "[result-column|AS column-alias]" syntax. SQLite allows you to create views that depend on automatically generated column names, but you should avoid using them since the rules used to generate column names are not a defined part of the interface and might change in future releases of SQLite. <p>The <yyterm>column-name</yyterm> list syntax was added in SQLite versions 3.9.0 ([dateof:3.9.0]). <tcl> |
Added pages/lang_createvtab.in.
> > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > | 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 | <title>CREATE VIRTUAL TABLE</title> <tcl> hd_keywords *createvtab {CREATE VIRTUAL TABLE} </tcl> <fancy_format> <tcl> RecursiveBubbleDiagram create-virtual-table-stmt </tcl> <p>A [virtual table] is an interface to an external storage or computation engine that appears to be a table but does not actually store information in the database file.</p> <p>In general, you can do anything with a [virtual table] that can be done with an ordinary table, except that ^you cannot create indices or triggers on a virtual table. ^Some virtual table implementations might impose additional restrictions. For example, many virtual tables are read-only.</p> <p>The <yyterm>module-name</yyterm> is the name of an object that implements the virtual table. ^The <yyterm>module-name</yyterm> must be registered with the SQLite database connection using [sqlite3_create_module()] or [sqlite3_create_module_v2()] prior to issuing the CREATE VIRTUAL TABLE statement. ^The module takes zero or more comma-separated arguments. ^The arguments can be just about any text as long as it has balanced parentheses. The argument syntax is sufficiently general that the arguments can be made to appear as [column definitions] in a traditional [CREATE TABLE] statement. ^SQLite passes the module arguments directly to the [xCreate] and [xConnect] methods of the module implementation without any interpretation. It is the responsibility of the module implementation to parse and interpret its own arguments.</p> <p>^A virtual table is destroyed using the ordinary [DROP TABLE] statement. There is no DROP VIRTUAL TABLE statement.</p> |
Added pages/lang_datefunc.in.
> > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > | 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60 61 62 63 64 65 66 67 68 69 70 71 72 73 74 75 76 77 78 79 80 81 82 83 84 85 86 87 88 89 90 91 92 93 94 95 96 97 98 99 100 101 102 103 104 105 106 107 108 109 110 111 112 113 114 115 116 117 118 119 120 121 122 123 124 125 126 127 128 129 130 131 132 133 134 135 136 137 138 139 140 141 142 143 144 145 146 147 148 149 150 151 152 153 154 155 156 157 158 159 160 161 162 163 164 165 166 167 168 169 170 171 172 173 174 175 176 177 178 179 180 181 182 183 184 185 186 187 188 189 190 191 192 193 194 195 196 197 198 199 200 201 202 203 204 205 206 207 208 209 210 211 212 213 214 215 216 217 218 219 220 221 222 223 224 225 226 227 228 229 230 231 232 233 234 235 236 237 238 239 240 241 242 243 244 245 246 247 248 249 250 251 252 253 254 255 256 257 258 259 260 261 262 263 264 265 266 267 268 269 270 271 272 273 274 275 276 277 278 279 280 281 282 283 284 285 286 287 288 289 290 291 292 293 294 295 296 297 298 299 300 301 302 303 304 305 306 307 308 309 310 | <title>Date And Time Functions</title> <tcl> hd_keywords *datefunc {date and time functions} {Date And Time Functions} hd_keywords {date() SQL function} {time() SQL function} hd_keywords {datetime() SQL function} {julianday() SQL function} hd_keywords {strftime() SQL function} </tcl> <table_of_contents> <h1>Overview</h1> <p> SQLite supports five date and time functions as follows: </p> <p> <ol> <li> ^(<b>date(</b><i>timestring, modifier, modifier, ...</i><b>)</b>)^ </li> <li> ^(<b>time(</b><i>timestring, modifier, modifier, ...</i><b>)</b>)^ </li> <li> ^(<b>datetime(</b><i>timestring, modifier, modifier, ...</i><b>)</b>)^ </li> <li> ^(<b>julianday(</b><i>timestring, modifier, modifier, ...</i><b>)</b>)^ </li> <li> ^(<b>strftime(</b><i>format, timestring, modifier, modifier, ...</i><b>)</b>)^ </li> </ol> <p> ^All five date and time functions take a time string as an argument. ^The time string is followed by zero or more modifiers. ^The strftime() function also takes a format string as its first argument. </p> <p> The date and time functions use a subset of [http://en.wikipedia.org/wiki/ISO_8601 | IS0-8601] date and time formats. ^The date() function returns the date in this format: YYYY-MM-DD. ^The time() function returns the time as HH:MM:SS. ^The datetime() function returns "YYYY-MM-DD HH:MM:SS". ^(The julianday() function returns the [http://en.wikipedia.org/wiki/Julian_day | Julian day] - the number of days since noon in Greenwich on November 24, 4714 B.C. ([http://en.wikipedia.org/wiki/Proleptic_Gregorian_calendar | Proleptic Gregorian calendar]).)^ ^The strftime() routine returns the date formatted according to the format string specified as the first argument. ^The format string supports the most common substitutions found in the [http://opengroup.org/onlinepubs/007908799/xsh/strftime.html | strftime() function] from the standard C library plus two new substitutions, %f and %J. ^(The following is a complete list of valid strftime() substitutions: </p> <blockquote> <table border="0" cellpadding="0" cellspacing="0"> <tr><td><td width="10"><td></tr> <tr><td> %d <td><td> day of month: 00 <tr><td> %f <td><td> fractional seconds: SS.SSS <tr><td> %H <td><td> hour: 00-24 <tr><td> %j <td><td> day of year: 001-366 <tr><td> %J <td><td> Julian day number <tr><td> %m <td><td> month: 01-12 <tr><td> %M <td><td> minute: 00-59 <tr><td> %s <td><td> seconds since 1970-01-01 <tr><td> %S <td><td> seconds: 00-59 <tr><td> %w <td><td> day of week 0-6 with Sunday==0 <tr><td> %W <td><td> week of year: 00-53 <tr><td> %Y <td><td> year: 0000-9999 <tr><td> %% <td><td> % </table> </blockquote>)^ <p> ^(Notice that all other date and time functions can be expressed in terms of strftime(): </p> <blockquote> <table border="0" cellpadding="0" cellspacing="0"> <tr><td><b>Function</b><td width="30"><td><b>Equivalent strftime()</b> <tr><td> date(...) <td><td> strftime('%Y-%m-%d', ...) <tr><td> time(...) <td><td> strftime('%H:%M:%S', ...) <tr><td> datetime(...) <td><td> strftime('%Y-%m-%d %H:%M:%S', ...) <tr><td> julianday(...) <td><td> strftime('%J', ...) </table> </blockquote>)^ <p> The only reasons for providing functions other than strftime() is for convenience and for efficiency. </p> <h1>Time Strings</h1> <p>^(A time string can be in any of the following formats:</p> <ol> <li> <i>YYYY-MM-DD</i> <li> <i>YYYY-MM-DD HH:MM</i> <li> <i>YYYY-MM-DD HH:MM:SS</i> <li> <i>YYYY-MM-DD HH:MM:SS.SSS</i> <li> <i>YYYY-MM-DD</i><b>T</b><i>HH:MM</i> <li> <i>YYYY-MM-DD</i><b>T</b><i>HH:MM:SS</i> <li> <i>YYYY-MM-DD</i><b>T</b><i>HH:MM:SS.SSS</i> <li> <i>HH:MM</i> <li> <i>HH:MM:SS</i> <li> <i>HH:MM:SS.SSS</i> <li> <b>now</b> <li> <i>DDDDDDDDDD</i> </ol>)^ <p> ^In formats 5 through 7, the "T" is a literal character separating the date and the time, as required by [http://www.w3c.org/TR/NOTE-datetime | ISO-8601]. ^Formats 8 through 10 that specify only a time assume a date of 2000-01-01. Format 11, the string 'now', is converted into the current date and time as obtained from the xCurrentTime method of the [sqlite3_vfs] object in use. ^The 'now' argument to date and time functions always returns exactly the same value for multiple invocations within the same [sqlite3_step()] call. ^[http://en.wikipedia.org/wiki/Coordinated_Universal_Time | Universal Coordinated Time (UTC)] is used. ^Format 12 is the [http://en.wikipedia.org/wiki/Julian_day | Julian day number] expressed as a floating point value. </p> <p> Formats 2 through 10 may be optionally followed by a timezone indicator of the form "<i>[+-]HH:MM</i>" or just "<i>Z</i>". The date and time functions use UTC or "zulu" time internally, and so the "Z" suffix is a no-op. Any non-zero "HH:MM" suffix is subtracted from the indicated date and time in order to compute zulu time. For example, all of the following time strings are equivalent: </p> <blockquote> 2013-10-07 08:23:19.120<br> 2013-10-07T08:23:19.120Z<br> 2013-10-07 04:23:19.120-04:00<br> 2456572.84952685 </blockquote> <p> ^(In formats 4, 7, and 10, the fractional seconds value SS.SSS can have one or more digits following the decimal point. Exactly three digits are shown in the examples because only the first three digits are significant to the result, but the input string can have fewer or more than three digits and the date/time functions will still operate correctly.)^ Similarly, format 12 is shown with 10 significant digits, but the date/time functions will really accept as many or as few digits as are necessary to represent the Julian day number. </p> <h1>Modifiers</h1> <p>^The time string can be followed by zero or more modifiers that alter date and/or time. ^Each modifier is a transformation that is applied to the time value to its left. ^Modifiers are applied from left to right; order is important. ^(The available modifiers are as follows.</p> <ol> <li> NNN days <li> NNN hours <li> NNN minutes <li> NNN.NNNN seconds <li> NNN months <li> NNN years <li> start of month <li> start of year <li> start of day <li> weekday N <li> unixepoch <li> localtime <li> utc </ol>)^ <p>^The first six modifiers (1 through 6) simply add the specified amount of time to the date and time specified by the preceding timestring and modifiers. ^The 's' character at the end of the modifier names is optional. ^Note that "±NNN months" works by rendering the original date into the YYYY-MM-DD format, adding the ±NNN to the MM month value, then normalizing the result. ^Thus, for example, the data 2001-03-31 modified by '+1 month' initially yields 2001-04-31, but April only has 30 days so the date is normalized to 2001-05-01. ^A similar effect occurs when the original date is February 29 of a leapyear and the modifier is ±N years where N is not a multiple of four.</p> <p>^The "start of" modifiers (7 through 9) shift the date backwards to the beginning of the current month, year or day.</p> <p>^(The "weekday" modifier advances the date forward, if necessary, to the next date where the weekday number is N. Sunday is 0, Monday is 1, and so forth.)^ ^If the date is already on the desired weekday, the "weekday" modifier leaves the date unchanged. </p> <p>^The "unixepoch" modifier (11) only works if it immediately follows a timestring in the DDDDDDDDDD format. ^This modifier causes the DDDDDDDDDD to be interpreted not as a Julian day number as it normally would be, but as [http://en.wikipedia.org/wiki/Unix_time | Unix Time] - the number of seconds since 1970. If the "unixepoch" modifier does not follow a timestring of the form DDDDDDDDDD which expresses the number of seconds since 1970 or if other modifiers separate the "unixepoch" modifier from prior DDDDDDDDDD then the behavior is undefined. For SQLite versions before 3.16.0 ([dateof:3.16.0]), the "unixepoch" modifier only works for dates between 0000-01-01 00:00:00 and 5352-11-01 10:52:47 (unix times of -62167219200 through 106751991167).</p> <tcl>hd_fragment localtime {localtime modifier} {'utc' modifier}</tcl> <p>^The "localtime" modifier (12) assumes the time string to its left is in Universal Coordinated Time (UTC) and adjusts the time string so that it displays localtime. If "localtime" follows a time that is not UTC, then the behavior is undefined. ^(The "utc" modifier is the opposite of "localtime". "utc" assumes that the string to its left is in the local timezone and adjusts that string to be in UTC.)^ If the prior string is not in localtime, then the result of "utc" is undefined.</p> <h1>Examples</h1> ^(<p>Compute the current date.<p> <blockquote>SELECT date('now');</blockquote>)^ ^(<p>Compute the last day of the current month.</p> <blockquote>SELECT date('now','start of month','+1 month','-1 day'); </blockquote>)^ ^(<p>Compute the date and time given a unix timestamp 1092941466.</p> <blockquote> SELECT datetime(1092941466, 'unixepoch'); </blockquote>)^ ^(<p>Compute the date and time given a unix timestamp 1092941466, and compensate for your local timezone.</p> <blockquote> SELECT datetime(1092941466, 'unixepoch', 'localtime'); </blockquote>)^ ^(<p>Compute the current unix timestamp.</p> <blockquote> SELECT strftime('%s','now'); </blockquote>)^ ^(<p>Compute the number of days since the signing of the US Declaration of Independence.</p> <blockquote> SELECT julianday('now') - julianday('1776-07-04'); </blockquote>)^ ^(<p>Compute the number of seconds since a particular moment in 2004:</p> <blockquote> SELECT strftime('%s','now') - strftime('%s','2004-01-01 02:34:56'); </blockquote>)^ ^(<p> Compute the date of the first Tuesday in October for the current year. </p> <blockquote> SELECT date('now','start of year','+9 months','weekday 2'); </blockquote>)^ ^(<p>Compute the time since the unix epoch in seconds (like strftime('%s','now') except includes fractional part):</p> <blockquote> SELECT (julianday('now') - 2440587.5)*86400.0; </blockquote>)^ <h1>Caveats And Bugs</h1> <p>The computation of local time depends heavily on the whim of politicians and is thus difficult to get correct for all locales. ^In this implementation, the standard C library function localtime_r() is used to assist in the calculation of local time. ^(The localtime_r() C function normally only works for years between 1970 and 2037. For dates outside this range, SQLite attempts to map the year into an equivalent year within this range, do the calculation, then map the year back.)^</p> <p>^(These functions only work for dates between 0000-01-01 00:00:00 and 9999-12-31 23:59:59 (julian day numbers 1721059.5 through 5373484.5).)^ For dates outside that range, the results of these functions are undefined.</p> <p>Non-Vista Windows platforms only support one set of DST rules. Vista only supports two. Therefore, on these platforms, historical DST calculations will be incorrect. For example, in the US, in 2007 the DST rules changed. Non-Vista Windows platforms apply the new 2007 DST rules to all previous years as well. Vista does somewhat better getting results correct back to 1986, when the rules were also changed.</p> <p>All internal computations assume the [http://en.wikipedia.org/wiki/Gregorian_calendar | Gregorian calendar] system. It is also assumed that every day is exactly 86400 seconds in duration.</p> |
Added pages/lang_delete.in.
> > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > | 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60 61 62 63 64 65 66 67 68 69 70 71 72 73 74 75 76 77 78 79 80 81 82 83 84 85 86 87 88 89 90 91 92 93 94 95 96 97 98 99 100 101 102 103 104 105 106 | <title>DELETE</title> <tcl> hd_keywords *delete DELETE DELETEs </tcl> <table_of_contents> <h1>Overview</h1> <tcl> RecursiveBubbleDiagram delete-stmt </tcl> <p>The DELETE command removes records from the table identified by the [qualified-table-name]. <p>^If the WHERE clause is not present, all records in the table are deleted. ^If a WHERE clause is supplied, then only those rows for which the WHERE clause [boolean expression] is true are deleted. ^Rows for which the expression is false or NULL are retained. <h1>Restrictions on DELETE Statements Within CREATE TRIGGER</h1> <p>The following restrictions apply to DELETE statements that occur within the body of a [CREATE TRIGGER] statement: <ul> <li><p>^The <yyterm>table-name</yyterm> specified as part of a DELETE statement within a trigger body must be unqualified. ^(In other words, the <i>schema-name</i><b>.</b> prefix on the table name is not allowed within triggers.)^ ^If the table to which the trigger is attached is not in the temp database, then DELETE statements within the trigger body must operate on tables within the same database as it. ^If the table to which the trigger is attached is in the TEMP database, then the unqualified name of the table being deleted is resolved in the same way as it is for a top-level statement (by searching first the TEMP database, then the main database, then any other databases in the order they were attached). <li><p>^The INDEXED BY and NOT INDEXED clauses are not allowed on DELETE statements within triggers.</p> <li><p>^The LIMIT and ORDER BY clauses (described below) are unsupported for DELETE statements within triggers.</p> </ul> <h1>Optional LIMIT and ORDER BY clauses</h1> <p>^(If SQLite is compiled with the [SQLITE_ENABLE_UPDATE_DELETE_LIMIT] compile-time option, then the syntax of the DELETE statement is extended by the addition of optional ORDER BY and LIMIT clauses:)^</p> <tcl>BubbleDiagram delete-stmt-limited</tcl> <p>^If a DELETE statement has a LIMIT clause, the maximum number of rows that will be deleted is found by evaluating the accompanying expression and casting it to an integer value. ^If the result of the evaluating the LIMIT clause cannot be losslessly converted to an integer value, it is an error. ^A negative LIMIT value is interpreted as "no limit". ^(If the DELETE statement also has an OFFSET clause, then it is similarly evaluated and cast to an integer value. Again, it is an error if the value cannot be losslessly converted to an integer.)^ ^If there is no OFFSET clause, or the calculated integer value is negative, the effective OFFSET value is zero. <p>^(If the DELETE statement has an ORDER BY clause, then all rows that would be deleted in the absence of the LIMIT clause are sorted according to the ORDER BY. The first <i>M</i> rows, where <i>M</i> is the value found by evaluating the OFFSET clause expression, are skipped, and the following <i>N</i>, where <i>N</i> is the value of the LIMIT expression, are deleted.)^ ^If there are less than <i>N</i> rows remaining after taking the OFFSET clause into account, or if the LIMIT clause evaluated to a negative value, then all remaining rows are deleted. <p>^If the DELETE statement has no ORDER BY clause, then all rows that would be deleted in the absence of the LIMIT clause are assembled in an arbitrary order before applying the LIMIT and OFFSET clauses to determine the subset that are actually deleted. <p>^(The ORDER BY clause on a DELETE statement is used only to determine which rows fall within the LIMIT. The order in which rows are deleted is arbitrary and is not influenced by the ORDER BY clause.)^ <tcl>hd_fragment truncateopt {truncate optimization}</tcl> <h1>The Truncate Optimization</h1> <p>^When the WHERE is omitted from a DELETE statement and the table being deleted has no triggers, SQLite uses an optimization to erase the entire table content without having to visit each row of the table individually. This "truncate" optimization makes the delete run much faster. Prior to SQLite [version 3.6.5] ([dateof:3.6.5]), the truncate optimization also meant that the [sqlite3_changes()] and [sqlite3_total_changes()] interfaces and the [count_changes pragma] will not actually return the number of deleted rows. That problem has been fixed as of [version 3.6.5] ([dateof:3.6.5]). <p>^The truncate optimization can be permanently disabled for all queries by recompiling SQLite with the [SQLITE_OMIT_TRUNCATE_OPTIMIZATION] compile-time switch.</p> <p>The truncate optimization can also be disabled at runtime using the [sqlite3_set_authorizer()] interface. ^If an authorizer callback returns [SQLITE_IGNORE] for an [SQLITE_DELETE] action code, then the DELETE operation will proceed but the truncate optimization will be bypassed and rows will be deleted one by one.</p> |
Added pages/lang_detach.in.
> > > > > > > > > > > > > > > > > > > > | 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 | <title>DETACH</title> <tcl> hd_keywords *detach *DETACH {DETACH DATABASE} </tcl> <fancy_format> <tcl> RecursiveBubbleDiagram detach-stmt </tcl> <p>^This statement detaches an additional database connection previously attached using the [ATTACH] statement. ^When not in [shared cache mode], it is possible to have the same database file attached multiple times using different names, and detaching one connection to a file will leave the others intact.</p> <p> ^In [shared cache mode], attempting to attach the same database file more than once results in an error. |
Added pages/lang_dropindex.in.
> > > > > > > > > > > > > > > > | 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 | <title>DROP INDEX</title> <tcl> hd_keywords *dropindex {DROP INDEX} </tcl> <fancy_format> <tcl> RecursiveBubbleDiagram drop-index-stmt </tcl> <p>^The DROP INDEX statement removes an index added with the [CREATE INDEX] statement. The index is completely removed from the disk. The only way to recover the index is to reenter the appropriate [CREATE INDEX] command.</p> <tcl> |
Added pages/lang_droptable.in.
> > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > | 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 | <title>DROP TABLE</title> <tcl> hd_keywords *droptable {DROP TABLE} </tcl> <fancy_format> <tcl> RecursiveBubbleDiagram drop-table-stmt </tcl> <p>^The DROP TABLE statement removes a table added with the [CREATE TABLE] statement. The name specified is the table name. ^The dropped table is completely removed from the database schema and the disk file. The table can not be recovered. ^All indices and triggers associated with the table are also deleted.</p> <p>^The optional IF EXISTS clause suppresses the error that would normally result if the table does not exist.</p> <p>^If [foreign key constraints] are enabled, a DROP TABLE command performs an implicit [DELETE | DELETE FROM] command before removing the table from the database schema. ^Any triggers attached to the table are dropped from the database schema before the implicit DELETE FROM is executed, so this cannot cause any triggers to fire. By contrast, ^an implicit DELETE FROM does cause any configured [foreign key actions] to take place. ^If the implicit DELETE FROM executed as part of a DROP TABLE command violates any immediate foreign key constraints, an error is returned and the table is not dropped. ^If the implicit DELETE FROM causes any deferred foreign key constraints to be violated, and the violations still exist when the transaction is committed, an error is returned at the time of commit. |
Added pages/lang_droptrigger.in.
> > > > > > > > > > > > > > > > | 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 | <title>DROP TRIGGER</title> <tcl> hd_keywords *droptrigger {DROP TRIGGER} </tcl> <tcl> RecursiveBubbleDiagram drop-trigger-stmt </tcl> <p>^The DROP TRIGGER statement removes a trigger created by the [CREATE TRIGGER] statement. ^Once removed, the trigger definition is no longer present in the sqlite_master (or sqlite_temp_master) table and is not fired by any subsequent INSERT, UPDATE or DELETE statements. <p>^Note that triggers are automatically dropped when the associated table is dropped. |
Added pages/lang_dropview.in.
> > > > > > > > > > > > > > > > > > > > > > > > > > | 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 | <title>DROP VIEW</title> <tcl> hd_keywords *dropview {DROP VIEW} </tcl> <fancy_format> <tcl> RecursiveBubbleDiagram drop-view-stmt </tcl> <p>^The DROP VIEW statement removes a view created by the [CREATE VIEW] statement. ^The view definition is removed from the database schema, but no actual data in the underlying base tables is modified. <p>^(The view to drop is identified by the view-name and optional schema-name specified as part of the DROP VIEW statement. This reference is resolved using the standard procedure for [object resolution].)^ <p> ^If the specified view cannot be found and the IF EXISTS clause is not present, it is an error. ^If the specified view cannot be found and an IF EXISTS clause is present in the DROP VIEW statement, then the statement is a no-op. <tcl> |
Added pages/lang_explain.in.
> > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > | 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60 61 62 | <title>EXPLAIN</title> <tcl> hd_keywords *explain EXPLAIN </tcl> <fancy_format> <h1>Syntax</h1> <tcl> BubbleDiagram sql-stmt </tcl> <h1>Description</h1> <p>^An SQL statement can be preceded by the keyword "EXPLAIN" or by the phrase "EXPLAIN QUERY PLAN". ^Either modification causes the SQL statement to behave as a query and to return information about how the SQL statement would have operated if the EXPLAIN keyword or phrase had been omitted.</p> <p>The output from EXPLAIN and EXPLAIN QUERY PLAN is intended for interactive analysis and troubleshooting only. The details of the output format are subject to change from one release of SQLite to the next. Applications should not use EXPLAIN or EXPLAIN QUERY PLAN since their exact behavior is variable and only partially documented.</p> <p>^When the EXPLAIN keyword appears by itself it causes the statement to behave as a query that returns the sequence of [virtual machine instructions] it would have used to execute the command had the EXPLAIN keyword not been present. ^When the EXPLAIN QUERY PLAN phrase appears, the statement returns high-level information regarding the query plan that would have been used. <p>The EXPLAIN QUERY PLAN command is described in [explain query plan|more detail here]. <h2>EXPLAIN operates at run-time, not at prepare-time</h2> <p>The EXPLAIN and EXPLAIN QUERY PLAN prefixes affect the behavior of running a [prepared statement] using [sqlite3_step()]. The process of generating a new prepared statement using [sqlite3_prepare()] or similar is (mostly) unaffected by EXPLAIN. (The exception to the previous sentence is that some special opcodes used by EXPLAIN QUERY PLAN are omitted when building an EXPLAIN QUERY PLAN prepared statement, as a performance optimization.) <p>This means that actions that occur during sqlite3_prepare() are unaffected by EXPLAIN. <ul> <li><p> Some [PRAGMA] statements do their work during sqlite3_prepare() rather than during sqlite3_step(). Those PRAGMA statements are unaffected by EXPLAIN. They operate the same with or without the EXPLAIN prefix. The set of PRAGMA statements that are unaffected by EXPLAIN can vary from one release to the next. Some PRAGMA statements operate during sqlite3_prepare() depending on their arguments. For consistent results, avoid using EXPLAIN on PRAGMA statements. <li><p> The [authorizer callback] is invoked regardless of the presence of EXPLAIN or EXPLAIN QUERY PLAN. </ul> |
Added pages/lang_expr.in.
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(COLLATE and "~" are associative so their binding order does not matter.) ^The collating sequence set by the COLLATE operator overrides the collating sequence determined by the COLLATE clause in a table [column definition]. See the [collating sequence| detailed discussion on collating sequences] in the [datatype | Datatype In SQLite3] document for additional information. </p> <tcl>hd_puts " <p>^The unary operator [Operator +] is a no-op. ^It can be applied to strings, numbers, blobs or NULL and it always returns a result with the same value as the operand.</p>"</tcl> <p>Note that there are two variations of the equals and not equals operators. ^Equals can be either <tcl> hd_puts "[Operator =] or [Operator ==]. ^The non-equals operator can be either [Operator !=] or [Operator {<>}]. ^The [Operator ||] operator is \"concatenate\" - it joins together the two strings of its operands. ^The operator [Operator %] outputs the integer value of its left operand modulo its right operand. In other words, the operator [Operator %] works in SQLite the same as it does in ANSI-C.</p> <p>^The result of any binary operator is either a numeric value or NULL, except for the [Operator ||] concatenation operator which always evaluates to either NULL or a text value.</p>" hd_fragment {isisnot} {IS operator} {IS NOT operator} hd_puts "<p>^The [Operator IS] and [Operator {IS NOT}] operators work like [Operator =] and [Operator !=] except when one or both of the operands are NULL. ^In this case, if both operands are NULL, then the IS operator evaluates to 1 (true) and the IS NOT operator evaluates to 0 (false). ^If one operand is NULL and the other is not, then the IS operator evaluates to 0 (false) and the IS NOT operator is 1 (true). ^It is not possible for an IS or IS NOT expression to evaluate to NULL. ^Operators [Operator IS] and [Operator {IS NOT}] have the same precedence as [Operator =]." <tcl>hd_fragment litvalue {literal value}</tcl> <h1>Literal Values (Constants)</h1> <p> A literal value represents a constant. ^Literal values may be integers, floating point numbers, strings, BLOBs, or NULLs. <p> The syntax for integer and floating point literals (collectively "numeric literals") is shown by the following diagram:</p> <tcl>BubbleDiagram numeric-literal</tcl> <p> ^(If a numeric literal has a decimal point or an exponentiation clause or if its magnitude is less than -9223372036854775808 or greater than 9223372036854775807, then it is a floating point literal. Otherwise is it is an integer literal.)^ ^The "E" character that begins the exponentiation clause of a floating point literal can be either upper or lower case. ^(The "." character is always used as the decimal point even if the locale setting specifies "," for this role - the use of "," for the decimal point would result in syntactic ambiguity.)^ <tcl>hd_fragment hexint {hexadecimal integer literals} {hexadecimal integers}</tcl> <p>^Hexadecimal integer literals follow the C-language notation of "0x" or "0X" followed by hexadecimal digits. ^For example, 0x1234 means the same as 4660 and 0x8000000000000000 means the same as -9223372036854775808. ^(Hexadecimal integer literals are interpreted as 64-bit two's-complement integers and are thus limited to sixteen significant digits of precision.)^ Support for hexadecimal integers was added to SQLite version 3.8.6 ([dateof:3.8.6]). ^For backwards compatibility, the "0x" hexadecimal integer notation is only understood by the SQL language parser, not by the type conversions routines. ^(String variables that contain text formatted like hexadecimal integers are not interpreted as hexadecimal integers when coercing the string value into an integer due to a [CAST expression] or for a [column affinity] transformation or prior to performing a numeric operation or for any other run-time conversions.)^ ^(When coercing a string value in the format of a hexadecimal integer into an integer value, the conversion process stops when the 'x' character is seen so the resulting integer value is always zero.)^ ^(SQLite only understands the hexadecimal integer notation when it appears in the SQL statement text, not when it appears as part of the content of the database.)^ <p> ^A string constant is formed by enclosing the string in single quotes ('). ^A single quote within the string can be encoded by putting two single quotes in a row - as in Pascal. C-style escapes using the backslash character are not supported because they are not standard SQL. <p> ^BLOB literals are string literals containing hexadecimal data and preceded by a single "x" or "X" character. ^(Example: X'53514C697465')^ <p> ^A literal value can also be the token "NULL". </p> <tcl>hd_fragment varparam parameter parameters {bound parameter} {bound parameters}</tcl> <h1>Parameters</h1> <p> A "variable" or "parameter" token specifies a placeholder in the expression for a value that is filled in at runtime using the [sqlite3_bind_blob() | sqlite3_bind()] family of C/C++ interfaces. Parameters can take several forms: </p> <blockquote> <table> <tr> <td align="right" valign="top"><b>?</b><i>NNN</i></td><td width="20"></td> <td>^(A question mark followed by a number <i>NNN</i> holds a spot for the NNN-th parameter. NNN must be between 1 and [SQLITE_MAX_VARIABLE_NUMBER].)^ </td> </tr> <tr> <td align="right" valign="top"><b>?</b></td><td width="20"></td> <td>^A question mark that is not followed by a number creates a parameter with a number one greater than the largest parameter number already assigned. ^If this means the parameter number is greater than [SQLITE_MAX_VARIABLE_NUMBER], it is an error. This parameter format is provided for compatibility with other database engines. But because it is easy to miscount the question marks, the use of this parameter format is discouraged. Programmers are encouraged to use one of the symbolic formats below or the ?NNN format above instead. </td> </tr> <tr> <td align="right" valign="top"><b>:</b><i>AAAA</i></td><td width="20"></td> <td>^A colon followed by an identifier name holds a spot for a [sqlite3_bind_parameter_name|named parameter] with the name :AAAA. ^(Named parameters are also numbered. The number assigned is one greater than the largest parameter number already assigned.)^ ^If this means the parameter would be assigned a number greater than [SQLITE_MAX_VARIABLE_NUMBER], it is an error. To avoid confusion, it is best to avoid mixing named and numbered parameters.</td> </tr> <tr> <td align="right" valign="top"><b>@</b><i>AAAA</i></td><td width="20"></td> <td>^An "at" sign works exactly like a colon, except that the name of the parameter created is @AAAA.</td> </tr> <tr> <td align="right" valign="top"><b>$</b><i>AAAA</i></td><td width="20"></td> <td>^A dollar-sign followed by an identifier name also holds a spot for a named parameter with the name $AAAA. ^(The identifier name in this case can include one or more occurrences of "::" and a suffix enclosed in "(...)" containing any text at all.)^ This syntax is the form of a variable name in the [http://www.tcl-lang.org/ | Tcl programming language]. The presence of this syntax results from the fact that SQLite is really a [Tcl extension] that has escaped into the wild.</td> </tr> </table> </blockquote> <p>^Parameters that are not assigned values using [sqlite3_bind_blob() | sqlite3_bind()] are treated as NULL. The [sqlite3_bind_parameter_index()] interface can be used to translate a symbolic parameter name into its equivalent numeric index.</p> <p>^The maximum parameter number is set at compile-time by the [SQLITE_MAX_VARIABLE_NUMBER] macro. ^(An individual [database connection] D can reduce its maximum parameter number below the compile-time maximum using the [sqlite3_limit](D, [SQLITE_LIMIT_VARIABLE_NUMBER],...) interface.)^ </p> <tcl>hd_fragment like LIKE ESCAPE</tcl> <h1>The LIKE, GLOB, REGEXP, and MATCH operators</h1> <p>^The LIKE operator does a pattern matching comparison. ^The operand to the right of the LIKE operator contains the pattern and the left hand operand contains the string to match against the pattern. <tcl>hd_puts "^A percent symbol (\"%\") in the LIKE pattern matches any sequence of zero or more characters in the string. ^An underscore (\"_\") in the LIKE pattern matches any single character in the string. ^(Any other character matches itself or its lower/upper case equivalent (i.e. case-insensitive matching).)^ <u>Important Note:</u> ^SQLite only understands upper/lower case for ASCII characters by default. ^The LIKE operator is case sensitive by default for unicode characters that are beyond the ASCII range. For example, ^the expression <b>'a' LIKE 'A'</b> is TRUE but <b>'æ' LIKE 'Æ'</b> is FALSE."</tcl> The ICU extension to SQLite includes an enhanced version of the LIKE operator that does case folding across all unicode characters.</p> <p>^If the optional ESCAPE clause is present, then the expression following the ESCAPE keyword must evaluate to a string consisting of a single character. ^This character may be used in the LIKE pattern to include literal percent or underscore characters. ^The escape character followed by a percent symbol (%), underscore (_), or a second instance of the escape character itself matches a literal percent symbol, underscore, or a single escape character, respectively. <p>^The infix LIKE operator is implemented by calling the application-defined SQL functions [like(<i>Y</i>,<i>X</i>)] or [like(<i>Y</i>,<i>X</i>,<i>Z</i>)]</a>.</p> <p>^The LIKE operator can be made case sensitive using the [case_sensitive_like pragma].</p> <tcl>hd_fragment glob GLOB</tcl> <p>^The GLOB operator is similar to LIKE but uses the Unix file globbing syntax for its wildcards. ^Also, GLOB is case sensitive, unlike LIKE. ^Both GLOB and LIKE may be preceded by the NOT keyword to invert the sense of the test. ^The infix GLOB operator is implemented by calling the function [glob(<i>Y</i>,<i>X</i>)] and can be modified by overriding that function.</p> <tcl>hd_fragment regexp REGEXP</tcl> <p>^The REGEXP operator is a special syntax for the regexp() user function. ^No regexp() user function is defined by default and so use of the REGEXP operator will normally result in an error message. ^If an [application-defined SQL function] named "regexp" is added at run-time, then the "<i>X</i> REGEXP <i>Y</i>" operator will be implemented as a call to "regexp(<i>Y</i>,<i>X</i>)".</p> <tcl>hd_fragment match MATCH</tcl> <p>^The MATCH operator is a special syntax for the match() application-defined function. ^The default match() function implementation raises an exception and is not really useful for anything. ^But extensions can override the match() function with more helpful logic.</p> <tcl>hd_fragment between BETWEEN</tcl> <h1>The BETWEEN operator</h1> <p>^(The BETWEEN operator is logically equivalent to a pair of comparisons. "<i>x</i> <b>BETWEEN</b> <i>y</i> <b>AND</b> <i>z</i>" is equivalent to "<i>x</i><b>>=</b><i>y</i> <b>AND</b> <i>x</i><b><=</b><i>z</i>" except that with BETWEEN, the <i>x</i> expression is only evaluated once.)^ ^The precedence of the BETWEEN operator is the same as the precedence as operators <b>==</b> and <b>!=</b> and <b>LIKE</b> and groups left to right. <tcl>hd_fragment case {CASE expression}</tcl> <h1>The CASE expression</h1> <p>A CASE expression serves a role similar to IF-THEN-ELSE in other programming languages. <p>The optional expression that occurs in between the CASE keyword and the first WHEN keyword is called the "base" expression. ^There are two basic forms of the CASE expression: those with a base expression and those without. <p>^In a CASE without a base expression, each WHEN expression is evaluated and the result treated as a boolean, starting with the leftmost and continuing to the right. ^The result of the CASE expression is the evaluation of the THEN expression that corresponds to the first WHEN expression that evaluates to true. ^Or, if none of the WHEN expressions evaluate to true, the result of evaluating the ELSE expression, if any. ^If there is no ELSE expression and none of the WHEN expressions are true, then the overall result is NULL. <p>^A NULL result is considered untrue when evaluating WHEN terms. <p>^In a CASE with a base expression, the base expression is evaluated just once and the result is compared against the evaluation of each WHEN expression from left to right. ^The result of the CASE expression is the evaluation of the THEN expression that corresponds to the first WHEN expression for which the comparison is true. ^Or, if none of the WHEN expressions evaluate to a value equal to the base expression, the result of evaluating the ELSE expression, if any. ^If there is no ELSE expression and none of the WHEN expressions produce a result equal to the base expression, the overall result is NULL. <p>^When comparing a base expression against a WHEN expression, the same collating sequence, affinity, and NULL-handling rules apply as if the base expression and WHEN expression are respectively the left- and right-hand operands of an <big><b>=</b></big> operator.</p> <p>^If the base expression is NULL then the result of the CASE is always the result of evaluating the ELSE expression if it exists, or NULL if it does not. <p>^Both forms of the CASE expression use lazy, or short-circuit, evaluation. <p>^(The only difference between the following two CASE expressions is that the <i>x</i> expression is evaluated exactly once in the first example but might be evaluated multiple times in the second: <ul><pre> <li>CASE x WHEN w1 THEN r1 WHEN w2 THEN r2 ELSE r3 END <li>CASE WHEN x=w1 THEN r1 WHEN x=w2 THEN r2 ELSE r3 END </pre></ul>)^ <tcl>hd_fragment in_op {IN operator} {NOT IN operator}</tcl> <h1>The IN and NOT IN operators</h1> <p>^The IN and NOT IN operators take an expression on the left and a list of values or a subquery on the right. ^When the right operand of an IN or NOT IN operator is a subquery, the subquery must have the same number of columns as there are columns in the [row value] of the left operand. ^The subquery on the right of an IN or NOT IN operator must be a scalar subquery if the left expression is not a [row value] expression. ^If the right operand of an IN or NOT IN operator is a list of values, each of those values must be scalars and the left expression must also be a scalar. ^The right-hand side of an IN or NOT IN operator can be a table <i>name</i> or [table-valued function] <i>name</i> in which case the right-hand side is understood to be subquery of the form "(SELECT * FROM <i>name</i>)". ^When the right operand is an empty set, the result of IN is false and the result of NOT IN is true, regardless of the left operand and even if the left operand is NULL. <p>^(The result of an IN or NOT IN operator is determined by the following matrix: <blockquote> <table border=1> <tr> <th>Left operand <br>is NULL <th>Right operand <br>contains NULL <th>Right operand <br>is an empty set <th>Left operand found <br>within right operand <th>Result of <br>IN operator <th>Result of <br>NOT IN operator <tr> <td align="center">no <td align="center">no <td align="center">no <td align="center">no <td align="center">false <td align="center">true <tr> <td align="center">does not matter <td align="center">no <td align="center">yes <td align="center">no <td align="center">false <td align="center">true <tr> <td align="center">no <td align="center">does not matter <td align="center">no <td align="center">yes <td align="center">true <td align="center">false <tr> <td align="center">no <td align="center">yes <td align="center">no <td align="center">no <td align="center">NULL <td align="center">NULL <tr> <td align="center">yes <td align="center">does not matter <td align="center">no <td align="center">does not matter <td align="center">NULL <td align="center">NULL </table> </blockquote>)^ <p>^Note that SQLite allows the parenthesized list of scalar values on the right-hand side of an IN or NOT IN operator to be an empty list but most other SQL database database engines and the SQL92 standard require the list to contain at least one element.</p> <h1>Table Column Names</h1> <p>^A column name can be any of the names defined in the [CREATE TABLE] statement or one of the following special identifiers: "<b>ROWID</b>", "<b>OID</b>", or "<b>_ROWID_</b>". ^The three special identifiers describe the unique integer key (the [rowid]) associated with every row of every table and so are not available on [WITHOUT ROWID] tables. ^The special identifiers only refer to the row key if the [CREATE TABLE] statement does not define a real column with the same name. ^The rowid can be used anywhere a regular column can be used.</p> <tcl>hd_fragment exists_op {EXISTS operator} {NOT EXISTS operator}</tcl> <h1>The EXISTS operator</h1> <p>^The EXISTS operator always evaluates to one of the integer values 0 and 1. ^If executing the SELECT statement specified as the right-hand operand of the EXISTS operator would return one or more rows, then the EXISTS operator evaluates to 1. ^If executing the SELECT would return no rows at all, then the EXISTS operator evaluates to 0. <p>^The number of columns in each row returned by the SELECT statement (if any) and the specific values returned have no effect on the results of the EXISTS operator. ^In particular, rows containing NULL values are not handled any differently from rows without NULL values. <tcl>hd_fragment subq {Subqueries}</tcl> <h1>Subquery Expressions</h1> <p>^A [SELECT] statement enclosed in parentheses is a subquery. ^All types of SELECT statement, including aggregate and compound SELECT queries (queries with keywords like UNION or EXCEPT) are allowed as scalar subqueries. ^The value of a subquery expression is the first row of the result from the enclosed [SELECT] statement. ^The value of a subquery expression is NULL if the enclosed [SELECT] statement returns no rows. <p>A subquery that returns a single column is a scalar subquery and can be used most anywhere. ^A subquery that returns two or more columns is a [row value] subquery and can only be used as the operand of a comparison operator. <tcl>hd_fragment cosub {correlated subqueries}</tcl> <h1>Correlated Subqueries</h1> <p>^A [SELECT] statement used as either a scalar subquery or as the right-hand operand of an IN, NOT IN or EXISTS expression may contain references to columns in the outer query. Such a subquery is known as a correlated subquery. ^A correlated subquery is reevaluated each time its result is required. ^An uncorrelated subquery is evaluated only once and the result reused as necessary. <tcl>hd_fragment castexpr {CAST expression} {CAST} {cast} {CAST operator}</tcl> <h1>CAST expressions</h1> <p>A CAST expression of the form "CAST(<i>expr</i> AS <i>type-name</i>)" is used to convert the value of <i>expr</i> to a different [storage class] specified by <yyterm>type-name</yyterm>. ^A CAST conversion is similar to the conversion that takes place when a [column affinity] is applied to a value except that with the CAST operator the conversion always takes place even if the conversion lossy and irreversible, whereas column affinity only changes the data type of a value if the change is lossless and reversible. <p>^If the value of <i>expr</i> is NULL, then the result of the CAST expression is also NULL. ^Otherwise, the storage class of the result is determined by applying the [rules for determining column affinity] to the <yyterm>type-name</yyterm>. <blockquote> <table border=1> <tr> <th> Affinity of <yyterm><nobr>type-name</nobr></yyterm> <th> Conversion Processing <tr> <td> NONE <td> ^Casting a value to a <yyterm>type-name</yyterm> with no affinity causes the value to be converted into a BLOB. ^Casting to a BLOB consists of first casting the value to TEXT in the [encoding] of the database connection, then interpreting the resulting byte sequence as a BLOB instead of as TEXT. <tr> <td> TEXT <td> ^To cast a BLOB value to TEXT, the sequence of bytes that make up the BLOB is interpreted as text encoded using the database encoding. <p> ^Casting an INTEGER or REAL value into TEXT renders the value as if via [sqlite3_snprintf()] except that the resulting TEXT uses the [encoding] of the database connection. <tr> <td> REAL <td> ^When casting a BLOB value to a REAL, the value is first converted to TEXT. <p>^When casting a TEXT value to REAL, the longest possible prefix of the value that can be interpreted as a real number is extracted from the TEXT value and the remainder ignored. ^Any leading spaces in the TEXT value are ignored when converging from TEXT to REAL. ^(If there is no prefix that can be interpreted as a real number, the result of the conversion is 0.0.)^ <tr> <td> INTEGER <td> ^When casting a BLOB value to INTEGER, the value is first converted to TEXT. <p>^When casting a TEXT value to INTEGER, the longest possible prefix of the value that can be interpreted as an integer number is extracted from the TEXT value and the remainder ignored. ^Any leading spaces in the TEXT value when converting from TEXT to INTEGER are ignored. ^If there is no prefix that can be interpreted as an integer number, the result of the conversion is 0. ^If the prefix integer is greater than +9223372036854775807 then the result of the cast is exactly +9223372036854775807. ^Similarly, if the prefix integer is less than -9223372036854775808 then the result of the cast is exactly -9223372036854775808. <p>^When casting to INTEGER, if the text looks like a floating point value with an exponent, the exponent will be ignored because it is no part of the integer prefix. ^For example, "(CAST '123e+5' AS INTEGER)" results in 123, not in 12300000. <p> ^(The CAST operator understands decimal integers only — conversion of [hexadecimal integers] stops at the "x" in the "0x" prefix of the hexadecimal integer string and thus result of the CAST is always zero.)^ <p>^A cast of a REAL value into an INTEGER results in the integer between the REAL value and zero that is closest to the REAL value. ^If a REAL is greater than the greatest possible signed integer (+9223372036854775807) then the result is the greatest possible signed integer and if the REAL is less than the least possible signed integer (-9223372036854775808) then the result is the least possible signed integer. <p>Prior to SQLite version 3.8.2 ([dateof:3.8.2]), casting a REAL value greater than +9223372036854775807.0 into an integer resulted in the most negative integer, -9223372036854775808. This behavior was meant to emulate the behavior of x86/x64 hardware when doing the equivalent cast. <tr> <td> NUMERIC <td> ^Casting a TEXT or BLOB value into NUMERIC yields either an INTEGER or a REAL result. ^If the input text looks like an integer (there is no decimal point nor exponent) and the value is small enough to fit in a 64-bit signed integer, then the result will be INTEGER. ^Input text that looks like floating point (there is a decimal point and/or an exponent) and the text describes a value that can be losslessly converted back and forth between IEEE 754 64-bit float and a 51-bit signed integer, then the result is INTEGER. (In the previous sentence, a 51-bit integer is specified since that is one bit less than the length of the mantissa of an IEEE 754 64-bit float and thus provides a 1-bit of margin for the text-to-float conversion operation.) ^Any text input that describes a value outside the range of a 64-bit signed integer yields a REAL result. <p> ^Casting a REAL or INTEGER value to NUMERIC is a no-op, even if a real value could be losslessly converted to an integer. </tr> </table> </blockquote> <p>^Note that the result from casting any non-BLOB value into a BLOB and the result from casting any BLOB value into a non-BLOB value may be different depending on whether the database [encoding] is UTF-8, UTF-16be, or UTF-16le. <tcl>hd_fragment booleanexpr {boolean expression}</tcl> <h1>Boolean Expressions</h1> <p>The SQL language features several contexts where an expression is evaluated and the result converted to a boolean (true or false) value. These contexts are: <ul> <li> the WHERE clause of a SELECT, UPDATE or DELETE statement, <li> the ON or USING clause of a join in a SELECT statement, <li> the HAVING clause of a SELECT statement, <li> the WHEN clause of an SQL trigger, and <li> the WHEN clause or clauses of some CASE expressions. </ul> <p>^(To convert the results of an SQL expression to a boolean value, SQLite first casts the result to a NUMERIC value in the same way as a [CAST expression]. A numeric zero value (integer value 0 or real value 0.0) is considered to be false. A NULL value is still NULL. All other values are considered true.)^ <p>^(For example, the values NULL, 0.0, 0, 'english' and '0' are all considered to be false.)^ ^(Values 1, 1.0, 0.1, -0.1 and '1english' are considered to be true.)^ <p>Beginning with SQLite 3.23.0 ([dateof:3.23.0]), SQLite recognizes the identifiers "TRUE" and "FALSE" as boolean literals, if and only if those identifiers are not already used for some other meaning. If there already exists columns or tables or other objects named TRUE or FALSE, then for the sake of backwards compatibility, the TRUE and FALSE identifiers refer to those other objects, not to the boolean values. <p>The boolean identifiers TRUE and FALSE are usually just aliases for the integer values 1 and 0, respectively. However, if TRUE or FALSE occur on the right-hand side of an IS operator, then they form new unary postfix operators "IS TRUE" and "IS FALSE" which test the boolean value of the operand on the left. <h1>Functions</h1> <p>SQLite supports many [corefunc|simple], [aggfunc|aggregate], and [window functions|window] SQL functions. For presentation purposes, simple functions are further subdivided into [corefunc | core functions], [datefunc|date-time functions], and [json1|JSON functions]. Applications can add new functions, written in C/C++, using the [sqlite3_create_function()] interface. </p> <p> The main expression bubble diagram above shows a single syntax for all function invocations. But this is merely to simplify the expression bubble diagram. In reality, each type of function has a slightly different syntax, shown below. The function invocation syntax shown in the main expression bubble diagram is the union of the three syntaxes shown here: <tcl> BubbleDiagram simple-function-invocation BubbleDiagram aggregate-function-invocation BubbleDiagram window-function-invocation </tcl> <p> The OVER clause is required for [window functions] and is prohibited otherwise. The DISTINCT keyword is only allowed in [aggfunc|aggregate functions]. The FILTER clause may not appear on a [corefunc|simple function]. <p>^It is possible to have an aggregate function with the same name as a simple function, as long as the number of arguments for the two forms of the function are different. ^For example, the [agg_max|max()] function with a single argument is an aggregate and the [max()] function with two or more arguments is a simple function. Aggregate functions can usually also be used as window functions. |
Added pages/lang_indexedby.in.
> > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > | 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60 61 62 63 64 65 66 67 68 69 70 | <title>The INDEXED BY Clause</title> <tcl> hd_keywords *langindexedby {INDEXED BY} {NOT INDEXED} </tcl> <fancy_format> <h1>How INDEXED BY Works</h1> <p>^The INDEXED BY phrase forces the [SQLite query planner] to use a particular named index on a [DELETE], [SELECT], or [UPDATE] statement. The INDEXED BY phrase is an SQLite extension and is not portable to other SQL database engines.</p> <tcl> RecursiveBubbleDiagram qualified-table-name </tcl> <p>^The "INDEXED BY <yyterm>index-name</yyterm>" phrase specifies that the named index must be used in order to look up values on the preceding table. ^If <yyterm>index-name</yyterm> does not exist or cannot be used for the query, then the preparation of the SQL statement fails. ^(The "NOT INDEXED" clause specifies that no index shall be used when accessing the preceding table, including implied indices create by UNIQUE and PRIMARY KEY constraints. However, the [rowid] can still be used to look up entries even when "NOT INDEXED" is specified.)^</p> <p>Some SQL database engines provide non-standard "hint" mechanisms which can be used to give the query optimizer clues about what indices it should use for a particular statement. The INDEX BY clause of SQLite is <em>not</em> a hinting mechanism and it should not be used as such. ^The INDEXED BY clause does not give the optimizer hints about which index to use; it gives the optimizer a requirement of which index to use. ^If the query optimizer is unable to use the index specified by the INDEX BY clause, then the query will fail with an error.</p> <p>The INDEXED BY clause is <em>not</em> intended for use in tuning the performance of a query. The intent of the INDEXED BY clause is to raise a run-time error if a schema change, such as dropping or creating an index, causes the query plan for a time-sensitive query to change. The INDEXED BY clause is designed to help detect undesirable query plan changes during regression testing. Application developers are admonished to omit all use of INDEXED BY during application design, implementation, testing, and tuning. If INDEXED BY is to be used at all, it should be inserted at the very end of the development process when "locking down" a design.</p> <h1>See Also</h1> <ol> <li><p>The [query planner checklist] describes steps that application developers should following to help resolve query planner problems. Notice the that the use of INDEXED BY is a last resort, to be used only when all other measures fail.</p> <li><p>[upluscontrol|The unary "+" operator] can be used to disqualify terms in the WHERE clause from use by indices. Careful use of unary + can sometimes help prevent the query planner from choosing a poor index without restricting it to using one specific index. Careful placement of unary + operators is a better method for controlling which indices are used by a query.</p> <li><p>The [sqlite3_stmt_status()] C/C++ interface together with the [SQLITE_STMTSTATUS_FULLSCAN_STEP] and [SQLITE_STMTSTATUS_SORT] verbs can be used to detect at run-time when an SQL statement is not making effective use of indices. Many applications may prefer to use the [sqlite3_stmt_status()] interface to detect index misuse rather than the INDEXED BY phrase described here.</p> </ol> |
Added pages/lang_insert.in.
> > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > | 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60 61 62 63 64 65 66 67 68 69 70 71 72 73 74 75 76 77 78 79 80 81 82 83 84 85 86 | <title>INSERT</title> <tcl> hd_keywords *insert INSERT *INSERTs </tcl> <fancy_format> <tcl> RecursiveBubbleDiagram insert-stmt </tcl> <p>The INSERT statement comes in three basic forms. <ol> <li><p><b>INSERT INTO </b><i>table</i><b> VALUES(...);</b> <p>^The first form (with the "VALUES" keyword) creates one or more new rows in an existing table. ^If the <yyterm>column-name</yyterm> list after <yyterm>table-name</yyterm> is omitted then the number of values inserted into each row must be the same as the number of columns in the table. ^In this case the result of evaluating the left-most expression from each term of the VALUES list is inserted into the left-most column of each new row, and so forth for each subsequent expression. ^If a <yyterm>column-name</yyterm> list is specified, then the number of values in each term of the VALUE list must match the number of specified columns. ^Each of the named columns of the new row is populated with the results of evaluating the corresponding VALUES expression. ^Table columns that do not appear in the column list are populated with the [default column value] (specified as part of the [CREATE TABLE] statement), or with NULL if no [default value] is specified. <li><p><b>INSERT INTO </b><i>table</i><b> SELECT ...;</b> <p>The second form of the INSERT statement contains a [SELECT] statement instead of a VALUES clause. ^A new entry is inserted into the table for each row of data returned by executing the SELECT statement. ^If a column-list is specified, the number of columns in the result of the SELECT must be the same as the number of items in the column-list. ^Otherwise, if no column-list is specified, the number of columns in the result of the SELECT must be the same as the number of columns in the table. ^Any SELECT statement, including [compound SELECTs] and SELECT statements with [ORDER BY] and/or [LIMIT] clauses, may be used in an INSERT statement of this form. <p>To avoid a parsing ambiguity, the SELECT statement should always contain a WHERE clause, even if that clause is simply "WHERE true", if the [upsert-clause] is present. Without the WHERE clause, the parser does not know if the token "ON" is part of a join constraint on the SELECT, or the beginning of the [upsert-clause]. <li><p><b>INSERT INTO </b><i>table</i><b> DEFAULT VALUES;</b> <p>The third form of an INSERT statement is with DEFAULT VALUES. ^(The INSERT ... DEFAULT VALUES statement inserts a single new row into the named table.)^ ^Each column of the new row is populated with its [default value], or with a NULL if no default value is specified as part of the column definition in the [CREATE TABLE] statement. The [upsert-clause] is not supported after DEFAULT VALUES. </ol> <p> ^The initial "INSERT" keyword can be replaced by "REPLACE" or "INSERT OR <i>action</i>" to specify an alternative constraint [ON CONFLICT|conflict resolution algorithm] to use during that one INSERT command. For compatibility with MySQL, ^the parser allows the use of the single keyword <a href="lang_replace.html">REPLACE</a> as an alias for "INSERT OR REPLACE". <p>^(The optional "<i>schema-name</i><b>.</b>" prefix on the <yyterm>table-name</yyterm> is supported for top-level INSERT statements only.)^ ^The table name must be unqualified for INSERT statements that occur within [CREATE TRIGGER] statements. ^Similarly, the "DEFAULT VALUES" form of the INSERT statement is supported for top-level INSERT statements only and not for INSERT statements within triggers. <p> <p>The optional "AS <yyterm>alias</yyterm>" phrase provides an alternative name for the table into which content is being inserted. The alias name can be used within WHERE and SET clauses of the [UPSERT]. If there is no [upsert-clause], then the <yyterm>alias</yyterm> is pointless, but also harmless. <p>See the separate [UPSERT] documentation for the additional trailing syntax that can cause an INSERT to behave as an UPDATE if the INSERT would otherwise violate a uniqueness constraint. The [upsert clause] is not allowed on an "INSERT ... DEFAULT VALUES". |
Added pages/lang_keywords.in.
> > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > | 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60 61 62 63 64 65 66 67 68 69 70 71 72 73 74 75 76 77 78 79 80 81 82 83 84 85 86 87 88 89 90 91 92 93 94 95 96 97 98 99 100 101 102 103 104 105 106 107 108 109 110 111 112 113 114 115 116 117 118 119 120 121 122 123 124 125 126 127 128 129 130 131 132 133 134 135 136 137 138 139 140 141 142 143 144 145 146 147 148 149 150 151 152 153 154 155 156 157 158 159 160 161 162 163 164 165 166 167 168 169 170 171 172 173 174 175 176 177 178 179 180 181 182 183 184 185 186 187 188 189 190 191 192 193 194 195 196 197 198 199 200 201 202 203 204 205 206 207 208 209 210 211 212 213 214 215 216 217 218 219 220 221 222 223 224 225 226 227 228 229 230 231 232 233 234 235 236 237 238 239 240 241 242 243 | <title>SQLite Keywords</title> <tcl> hd_keywords *langkeywords {SQLite Keywords} keywords \ {*SQL keyword} {SQL keywords} set keyword_list [lsort { ABORT ACTION ADD AFTER ALL ALTER ALWAYS ANALYZE AND AS ASC ATTACH AUTOINCREMENT BEFORE BEGIN BETWEEN BY CASCADE CASE CAST CHECK COLLATE COLUMN COMMIT CONFLICT CONSTRAINT CREATE CROSS CURRENT CURRENT_DATE CURRENT_TIME CURRENT_TIMESTAMP DATABASE DEFAULT DEFERRED DEFERRABLE DELETE DESC DETACH DISTINCT DO DROP END EACH ELSE ESCAPE EXCEPT EXCLUSIVE EXCLUDE EXISTS EXPLAIN FAIL FILTER FIRST FOLLOWING FOR FOREIGN FROM FULL GENERATED GLOB GROUP GROUPS HAVING IF IGNORE IMMEDIATE IN INDEX INDEXED INITIALLY INNER INSERT INSTEAD INTERSECT INTO IS ISNULL JOIN KEY LAST LEFT LIKE LIMIT MATCH NATURAL NO NOT NOTHING NOTNULL NULL NULLS OF OFFSET ON OR ORDER OTHERS OUTER OVER PARTITION PLAN PRAGMA PRECEDING PRIMARY QUERY RAISE RANGE RECURSIVE REFERENCES REGEXP REINDEX RELEASE RENAME REPLACE RESTRICT RIGHT ROLLBACK ROW ROWS SAVEPOINT SELECT SET TABLE TEMP TEMPORARY THEN TIES TO TRANSACTION TRIGGER UNBOUNDED UNION UNIQUE UPDATE USING VACUUM VALUES VIEW VIRTUAL WHEN WHERE WINDOW WITH WITHOUT }] </tcl> <fancy_format> <p>The SQL standard specifies a large number of keywords which may not be used as the names of tables, indices, columns, databases, user-defined functions, collations, virtual table modules, or any other named object. The list of keywords is so long that few people can remember them all. For most SQL code, your safest bet is to never use any English language word as the name of a user-defined object.</p> <p>If you want to use a keyword as a name, you need to quote it. There are four ways of quoting keywords in SQLite:</p> <p> <blockquote> <table> <tr> <td valign="top"><b>'keyword'</b></td><td width="20"></td> <td>^A keyword in single quotes is a string literal.</td></tr> <tr> <td valign="top"><b>"keyword"</b></td><td></td> <td>^A keyword in double-quotes is an identifier.</td></tr> <tr> <td valign="top"><b>[keyword]</b></td><td></td> <td>^A keyword enclosed in square brackets is an identifier. This is not standard SQL. This quoting mechanism is used by MS Access and SQL Server and is included in SQLite for compatibility.</td></tr> <tr> <td valign="top"><b>`keyword`</b></td><td></td> <td>^A keyword enclosed in grave accents (ASCII code 96) is an identifier. This is not standard SQL. This quoting mechanism is used by MySQL and is included in SQLite for compatibility.</td></tr> </table> </blockquote> </p> <p>For resilience when confronted with historical SQL statements, SQLite will sometimes bend the quoting rules above:</p> <ul> <li><p>^If a keyword in single quotes (ex: <b>'key'</b> or <b>'glob'</b>) is used in a context where an identifier is allowed but where a string literal is not allowed, then the token is understood to be an identifier instead of a string literal. </p></li> <li><p>^If a keyword in double quotes (ex: <b>"key"</b> or <b>"glob"</b>) is used in a context where it cannot be resolved to an identifier but where a string literal is allowed, then the token is understood to be a string literal instead of an identifier.</p></li> </ul> <p>Programmers are cautioned not to use the two exceptions described in the previous bullets. We emphasize that they exist only so that old and ill-formed SQL statements will run correctly. Future versions of SQLite might raise errors instead of accepting the malformed statements covered by the exceptions above.</p> <p> SQLite adds new keywords from time to time when it takes on new features. So to prevent your code from being broken by future enhancements, you should normally quote any identifier that is an English language word, even if you do not have to. </p> <p> The list below shows all possible keywords used by any build of SQLite regardless of [compile-time options]. Most reasonable configurations use most or all of these keywords, but some keywords may be omitted when SQL language features are disabled. Applications can use the [sqlite3_keyword_count()], [sqlite3_keyword_name()], and [sqlite3_keyword_check()] interfaces to determine the keywords recognized by SQLite at run-time. ^(Regardless of the compile-time configuration, any identifier that is not on the following <tcl>hd_puts [llength $keyword_list]</tcl> element list is not a keyword to the SQL parser in SQLite: </p> <div class="columns" style="columns:11em auto;"> <ul style="padding-top:0;"> <tcl> set lx {} foreach word [lsort $keyword_list] { hd_putsnl "<li>$word</li>" } hd_putsnl "</ul></div>)^" </tcl> |
Added pages/lang_naming.in.
> > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > | 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 | <title>Database Object Name Resolution</title> <tcl> hd_keywords *naming {object resolution} </tcl> <p> In SQLite, a database object (a table, index, trigger or view) is identified by the name of the object and the name of the database that it resides in. Database objects may reside in the main database, the temp database, or in an [ATTACH|attached database]. <p> The syntax of the [DROP TABLE], [DROP INDEX], [DROP VIEW], [DROP TRIGGER], [REINDEX], [ALTER TABLE] and many other commands all permit the user to specify a database object either by its name alone, or by a combination of its name and the name of its database. ^(If no database is specified as part of the object reference, then SQLite searches the main, temp and all attached databases for an object with a matching name. The temp database is searched first, followed by the main database, followed all attached databases in the order that they were attached. The reference resolves to the first match found.)^ For example: <pre>^( /* Add a table named 't1' to the temp, main and an attached database */ ATTACH 'file.db' AS aux; CREATE TABLE t1(x, y); CREATE TEMP TABLE t1(x, y); CREATE TABLE aux.t1(x, y); DROP TABLE t1; /* Drop table in temp database */ DROP TABLE t1; /* Drop table in main database */ DROP TABLE t1; /* Drop table in aux database */ )^</pre> <p> ^If a schema name is specified as part of an object reference, it must be either "main", or "temp" or the schema-name of an attached database. ^Like other SQL identifiers, schema names are case-insensitive. ^If a schema name is specified, then only that one schema is searched for the named object. <p> Most object references may only resolve to a specific type of object (for example a reference that is part of a DROP TABLE statement may only resolve to a table object, not an index, trigger or view). However in some contexts (e.g. [REINDEX]) an object reference may be resolve to more than one type of object. ^When searching database schemas for a named object, objects of types that cannot be used in the context of the reference are always ignored. |
Added pages/lang_reindex.in.
> > > > > > > > > > > > > > > > > > > > > > > > > > > > > > | 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 | <title>REINDEX</title> <tcl> hd_keywords *reindex REINDEX </tcl> <fancy_format> <tcl> RecursiveBubbleDiagram reindex-stmt </tcl> <p>^The REINDEX command is used to delete and recreate indices from scratch. This is useful when the definition of a collation sequence has changed. </p> <p>^If the REINDEX keyword is not followed by a collation-sequence or database object identifier, then all indices in all attached databases are rebuilt. <p>^If the REINDEX keyword is followed by a collation-sequence name, then all indices in all attached databases that use the named collation sequences are recreated. <p>^Or, if the argument attached to the REINDEX identifies a specific database table, then all indices attached to the database table are rebuilt. ^If it identifies a specific database index, then just that index is recreated. <p>^For a command of the form "REINDEX <i>name</i>", a match against <yyterm>collation-name</yyterm> takes precedence over a match against <yyterm>index-name</yyterm> or <yyterm>table-name</yyterm>. This ambiguity in the syntax may be avoided by always specifying a <yyterm>schema-name</yyterm> when reindexing a specific table or index. |
Added pages/lang_replace.in.
> > > > > > > > > > | 1 2 3 4 5 6 7 8 9 10 | <title>REPLACE</title> <tcl> hd_keywords *langreplace REPLACE </tcl> <fancy_format> <p>^The REPLACE command is an alias for the "[ON CONFLICT | INSERT OR REPLACE]" variant of the [INSERT] command. This alias is provided for compatibility other SQL database engines. See the [INSERT] command documentation for additional information.</p> |
Added pages/lang_select.in.
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The result of a SELECT is zero or more rows of data where each row has a fixed number of columns. A SELECT statement does not make any changes to the database. <p>The "[select-stmt]" syntax diagram above attempts to show as much of the SELECT statement syntax as possible in a single diagram, because some readers find that helpful. The following "[factored-select-stmt]" is an alternative syntax diagrams that expresses the same syntax but tries to break the syntax down into smaller chunks. <tcl> RecursiveBubbleDiagram --initially-hidden factored-select-stmt select-core </tcl> <p>Note that there are paths through the syntax diagrams that are not allowed in practice. Some examples: <ul> <li>A [VALUES] clause can be the first element in a [compound SELECT] that uses a [WITH] clause, but a [simple SELECT] that consists of just a [VALUES] clause cannot be preceded by a [WITH] clause. <li>The [WITH] clause must occur on the first SELECT of a [compound SELECT]. It cannot follow a [compound-operator]. </ul> <p>These and other similar syntax restrictions are described in the text. <p>The SELECT statement is the most complicated command in the SQL language. To make the description easier to follow, some of the passages below describe the way the data returned by a SELECT statement is determined as a series of steps. It is important to keep in mind that this is purely illustrative - in practice neither SQLite nor any other SQL engine is required to follow this or any other specific process. <tcl>hd_fragment simpleselect {simple SELECT}</tcl> <h1>Simple Select Processing</h1> <p>The core of a SELECT statement is a "simple SELECT" shown by the [select-core] and [simple-select-stmt] syntax diagrams below. In practice, most SELECT statements are simple SELECT statements. <tcl> RecursiveBubbleDiagram simple-select-stmt select-core </tcl> <p>Generating the results of a simple SELECT statement is presented as a four step process in the description below: <ol> <li> <p>[FROM clause] processing: The input data for the simple SELECT is determined. The input data is either implicitly a single row with 0 columns (if there is no FROM clause) or is determined by the FROM clause. <li> <p>[WHERE clause] processing: The input data is filtered using the WHERE clause expression. <li> <p>[GROUP BY|GROUP BY, HAVING and result-column expression] processing: The set of result rows is computed by aggregating the data according to any GROUP BY clause and calculating the result-set expressions for the rows of the filtered input dataset. <li> <p>[DISTINCT|DISTINCT/ALL keyword] processing: If the query is a "SELECT DISTINCT" query, duplicate rows are removed from the set of result rows. </ol> <p>There are two types of simple SELECT statement - aggregate and non-aggregate queries. ^A simple SELECT statement is an aggregate query if it contains either a GROUP BY clause or one or more aggregate functions in the result-set. ^Otherwise, if a simple SELECT contains no aggregate functions or a GROUP BY clause, it is a non-aggregate query. <p><b>1. Determination of input data (FROM clause processing).</b> <tcl>hd_fragment fromclause</tcl> <tcl>hd_keywords {FROM clause}</tcl> <p>The input data used by a simple SELECT query is a set of <i>N</i> rows each <i>M</i> columns wide. <p>^(If the FROM clause is omitted from a simple SELECT statement, then the input data is implicitly a single row zero columns wide)^ (i.e. <i>N</i>=1 and <i>M</i>=0). <p>If a FROM clause is specified, the data on which a simple SELECT query operates comes from the one or more tables or subqueries (SELECT statements in parentheses) specified following the FROM keyword. ^A subquery specified in the <yyterm>table-or-subquery</yyterm> following the FROM clause in a simple SELECT statement is handled as if it was a table containing the data returned by executing the subquery statement. ^Each column of the subquery has the [collation|collation sequence] and [affinity] of the corresponding expression in the subquery statement. <p>^If there is only a single table or subquery in the FROM clause, then the input data used by the SELECT statement is the contents of the named table. ^If there is more than one table or subquery in FROM clause then the contents of all tables and/or subqueries are joined into a single dataset for the simple SELECT statement to operate on. Exactly how the data is combined depends on the specific [join-operator] and [join-constraint] used to connect the tables or subqueries together. <p>All joins in SQLite are based on the cartesian product of the left and right-hand datasets. ^The columns of the cartesian product dataset are, in order, all the columns of the left-hand dataset followed by all the columns of the right-hand dataset. ^There is a row in the cartesian product dataset formed by combining each unique combination of a row from the left-hand and right-hand datasets. ^(In other words, if the left-hand dataset consists of <i>N<sub><small>left</small></sub></i> rows of <i>M<sub><small>left</small></sub></i> columns, and the right-hand dataset of <i>N<sub><small>right</small></sub></i> rows of <i>M<sub><small>right</small></sub></i> columns, then the cartesian product is a dataset of <i>N<sub><small>left</small></sub>×N<sub><small>right</small></sub></i> rows, each containing <i>M<sub><small>left</small></sub>+M<sub><small>right</small></sub></i> columns.)^ <p>^If the join-operator is "CROSS JOIN", "INNER JOIN", "JOIN" or a comma (",") and there is no ON or USING clause, then the result of the join is simply the cartesian product of the left and right-hand datasets. If join-operator does have ON or USING clauses, those are handled according to the following bullet points: <ul> <li> <p>^(If there is an ON clause then the ON expression is evaluated for each row of the cartesian product as a [boolean expression]. Only rows for which the expression evaluates to true are included from the dataset.)^ <li> <p>^If there is a USING clause then each of the column names specified must exist in the datasets to both the left and right of the join-operator. ^(For each pair of named columns, the expression "lhs.X = rhs.X" is evaluated for each row of the cartesian product as a [boolean expression]. Only rows for which all such expressions evaluates to true are included from the result set.)^ ^When comparing values as a result of a USING clause, the normal rules for handling affinities, collation sequences and NULL values in comparisons apply. ^The column from the dataset on the left-hand side of the join-operator is considered to be on the left-hand side of the comparison operator (=) for the purposes of collation sequence and affinity precedence. <p>^For each pair of columns identified by a USING clause, the column from the right-hand dataset is omitted from the joined dataset. ^This is the only difference between a USING clause and its equivalent ON constraint. <li> <p>^(If the NATURAL keyword is in the join-operator then an implicit USING clause is added to the join-constraints. The implicit USING clause contains each of the column names that appear in both the left and right-hand input datasets.)^ ^If the left and right-hand input datasets feature no common column names, then the NATURAL keyword has no effect on the results of the join. ^A USING or ON clause may not be added to a join that specifies the NATURAL keyword. <li> <p>^(If the join-operator is a "LEFT JOIN" or "LEFT OUTER JOIN", then after the ON or USING filtering clauses have been applied, an extra row is added to the output for each row in the original left-hand input dataset that corresponds to no rows at all in the composite dataset (if any).)^ ^The added rows contain NULL values in the columns that would normally contain values copied from the right-hand input dataset. </ul> <p>^(When more than two tables are joined together as part of a FROM clause, the join operations are processed in order from left to right. In other words, the FROM clause (A join-op-1 B join-op-2 C) is computed as ((A join-op-1 B) join-op-2 C).)^ <tcl>hd_fragment crossjoin {treats the CROSS JOIN operator specially}</tcl> <p><b>Side note: Special handling of CROSS JOIN.</b> ^There is no difference between the "INNER JOIN", "JOIN" and "," join operators. They are completely interchangeable in SQLite. ^(The "CROSS JOIN" join operator produces the same result as the "INNER JOIN", "JOIN" and "," operators)^, but is [CROSS JOIN|handled differently by the query optimizer] in that it prevents the query optimizer from reordering the tables in the join. An application programmer can use the CROSS JOIN operator to directly influence the algorithm that is chosen to implement the SELECT statement. Avoid using CROSS JOIN except in specific situations where manual control of the query optimizer is desired. Avoid using CROSS JOIN early in the development of an application as doing so is a <a href="http://c2.com/cgi/wiki?PrematureOptimization">premature optimization</a>. The special handling of CROSS JOIN is an SQLite-specific feature and is not a part of standard SQL. <tcl>hd_fragment whereclause</tcl> <tcl>hd_keywords {WHERE clause}</tcl> <p><b>2. WHERE clause filtering.</b> <p>^(If a WHERE clause is specified, the WHERE expression is evaluated for each row in the input data as a [boolean expression]. Only rows for which the WHERE clause expression evaluates to true are included from the dataset before continuing.)^ Rows are excluded from the result if the WHERE clause evaluates to either false or NULL. <p>For a JOIN or INNER JOIN or CROSS JOIN, there is no difference between a constraint expression in the WHERE clause and one in the ON clause. However, for a LEFT JOIN or LEFT OUTER JOIN, the difference is very important. In a LEFT JOIN, the extra NULL row for the right-hand table is added after ON clause processing but before WHERE clause processing. A constraint of the form "left.x=right.y" in an ON clause will therefore allow through the added all-NULL rows of the right table. But if that same constraint is in the WHERE clause a NULL in "right.y" will prevent the expression "left.x=right.y" from being true, and thus exclude that row from the output. <p><b>3. Generation of the set of result rows.</b> <tcl>hd_fragment resultset</tcl> <tcl>hd_keywords {result-set expressions} {GROUP BY}</tcl> <p>Once the input data from the FROM clause has been filtered by the WHERE clause expression (if any), the set of result rows for the simple SELECT are calculated. Exactly how this is done depends on whether the simple SELECT is an aggregate or non-aggregate query, and whether or not a GROUP BY clause was specified. <p> The list of expressions between the SELECT and FROM keywords is known as the result expression list. ^If a result expression is the special expression "*" then all columns in the input data are substituted for that one expression. ^(If the expression is the alias of a table or subquery in the FROM clause followed by ".*" then all columns from the named table or subquery are substituted for the single expression.)^ ^(It is an error to use a "*" or "alias.*" expression in any context other than a result expression list.)^ ^(It is also an error to use a "*" or "alias.*" expression in a simple SELECT query that does not have a FROM clause.)^ <p> ^(The number of columns in the rows returned by a simple SELECT statement is equal to the number of expressions in the result expression list after substitution of * and alias.* expressions.)^ Each result row is calculated by evaluating the expressions in the result expression list with respect to a single row of input data or, for aggregate queries, with respect to a group of rows. <ul> <li><p>^If the SELECT statement is <b>a non-aggregate query</b>, then each expression in the result expression list is evaluated for each row in the dataset filtered by the WHERE clause. <li><p>^If the SELECT statement is <b>an aggregate query without a GROUP BY</b> clause, then each aggregate expression in the result-set is evaluated once across the entire dataset. ^Each non-aggregate expression in the result-set is evaluated once for an arbitrarily selected row of the dataset. ^The same arbitrarily selected row is used for each non-aggregate expression. ^Or, if the dataset contains zero rows, then each non-aggregate expression is evaluated against a row consisting entirely of NULL values. <p>^The single row of result-set data created by evaluating the aggregate and non-aggregate expressions in the result-set forms the result of an aggregate query without a GROUP BY clause. ^An aggregate query without a GROUP BY clause always returns exactly one row of data, even if there are zero rows of input data. <li><p>^(If the SELECT statement is <b>an aggregate query with a GROUP BY</b> clause, then each of the expressions specified as part of the GROUP BY clause is evaluated for each row of the dataset. Each row is then assigned to a "group" based on the results; rows for which the results of evaluating the GROUP BY expressions are the same get assigned to the same group.)^ ^For the purposes of grouping rows, NULL values are considered equal. ^The usual rules for [collation|selecting a collation sequence] with which to compare text values apply when evaluating expressions in a GROUP BY clause. ^The expressions in the GROUP BY clause do <em>not</em> have to be expressions that appear in the result. ^The expressions in a GROUP BY clause may not be aggregate expressions. <p>^(If a HAVING clause is specified, it is evaluated once for each group of rows as a [boolean expression]. If the result of evaluating the HAVING clause is false, the group is discarded.)^ ^If the HAVING clause is an aggregate expression, it is evaluated across all rows in the group. ^If a HAVING clause is a non-aggregate expression, it is evaluated with respect to an arbitrarily selected row from the group. ^The HAVING expression may refer to values, even aggregate functions, that are not in the result.</p> <p>^Each expression in the result-set is then evaluated once for each group of rows. ^If the expression is an aggregate expression, it is evaluated across all rows in the group. ^Otherwise, it is evaluated against a single arbitrarily chosen row from within the group. ^If there is more than one non-aggregate expression in the result-set, then all such expressions are evaluated for the same row. <p>^Each group of input dataset rows contributes a single row to the set of result rows. ^Subject to filtering associated with the DISTINCT keyword, the number of rows returned by an aggregate query with a GROUP BY clause is the same as the number of groups of rows produced by applying the GROUP BY and HAVING clauses to the filtered input dataset. </ul> <tcl>hd_fragment bareagg {bare aggregate terms}</tcl> <p><b>Side note: Bare columns in an aggregate queries.</b> The usual case is that all column names in an aggregate query are either arguments to [aggfunc|aggregate functions] or else appear in the GROUP BY clause. A result column which contains a column name that is not within an aggregate function and that does not appear in the GROUP BY clause (if one exists) is called a "bare" column. Example: <blockquote><pre> SELECT a, b, sum(c) FROM tab1 GROUP BY a; </pre></blockquote> <p>In the query above, the "a" column is part of the GROUP BY clause and so each row of the output contains one of the distinct values for "a". The "c" column is contained within the [sum()] aggregate function and so that output column is the sum of all "c" values in rows that have the same value for "a". But what is the result of the bare column "b"? The answer is that the "b" result will be the value for "b" in one of the input rows that form the aggregate. The problem is that you usually do not know which input row is used to compute "b", and so in many cases the value for "b" is undefined. </p> <p> Special processing occurs when the aggregate function is either [maxAggFunc|min()] or [minAggFunc|max()]. Example: <blockquote><pre> SELECT a, b, max(c) FROM tab1 GROUP BY a; </pre></blockquote> <p>When the [maxAggFunc|min()] or [minAggFunc|max()] aggregate functions are used in an aggregate query, all bare columns in the result set take values from the input row which also contains the minimum or maximum. So in the query above, the value of the "b" column in the output will be the value of the "b" column in the input row that has the largest "c" value. There is still an ambiguity if two or more of the input rows have the same minimum or maximum value or if the query contains more than one min() and/or max() aggregate function. Only the built-in [minAggFunc|min()] and [maxAggFunc|max()] functions work this way. </p> <p><b>4. Removal of duplicate rows (DISTINCT processing).</b> <tcl>hd_fragment distinct</tcl> <tcl>hd_keywords {DISTINCT}</tcl> <p>^One of the ALL or DISTINCT keywords may follow the SELECT keyword in a simple SELECT statement. ^If the simple SELECT is a SELECT ALL, then the entire set of result rows are returned by the SELECT. ^If neither ALL or DISTINCT are present, then the behavior is as if ALL were specified. ^If the simple SELECT is a SELECT DISTINCT, then duplicate rows are removed from the set of result rows before it is returned. ^For the purposes of detecting duplicate rows, two NULL values are considered to be equal. ^The [how collation is determined|usual rules] apply for selecting a collation sequence to compare text values. <tcl> hd_fragment compound {compound select} {compound query} {compound SELECT} {compound SELECTs} </tcl> <h1>Compound Select Statements</h1> <p>Two or more [simple SELECT] statements may be connected together to form a compound SELECT using the UNION, UNION ALL, INTERSECT or EXCEPT operator, as shown by the following diagram: <tcl> RecursiveBubbleDiagram compound-select-stmt </tcl> <p>^In a compound SELECT, all the constituent SELECTs must return the same number of result columns. ^As the components of a compound SELECT must be simple SELECT statements, they may not contain [ORDER BY] or [LIMIT] clauses. ^[ORDER BY] and [LIMIT] clauses may only occur at the end of the entire compound SELECT, and then only if the final element of the compound is not a [VALUES] clause. <p>^A compound SELECT created using UNION ALL operator returns all the rows from the SELECT to the left of the UNION ALL operator, and all the rows from the SELECT to the right of it. ^The UNION operator works the same way as UNION ALL, except that duplicate rows are removed from the final result set. ^The INTERSECT operator returns the intersection of the results of the left and right SELECTs. ^The EXCEPT operator returns the subset of rows returned by the left SELECT that are not also returned by the right-hand SELECT. ^Duplicate rows are removed from the results of INTERSECT and EXCEPT operators before the result set is returned. <p>^For the purposes of determining duplicate rows for the results of compound SELECT operators, NULL values are considered equal to other NULL values and distinct from all non-NULL values. ^The collation sequence used to compare two text values is determined as if the columns of the left and right-hand SELECT statements were the left and right-hand operands of the equals (=) operator, except that greater precedence is not assigned to a collation sequence specified with the postfix COLLATE operator. ^No affinity transformations are applied to any values when comparing rows as part of a compound SELECT. <p>^(When three or more simple SELECTs are connected into a compound SELECT, they group from left to right. In other words, if "A", "B" and "C" are all simple SELECT statements, (A op B op C) is processed as ((A op B) op C).)^ </p> <tcl>hd_fragment orderby {order by} {ORDER BY}</tcl> <h1>The ORDER BY clause</h1> <p>If a SELECT statement that returns more than one row does not have an ORDER BY clause, the order in which the rows are returned is undefined. Or, if a SELECT statement does have an ORDER BY clause, then the list of expressions attached to the ORDER BY determine the order in which rows are returned to the user. <p> ^In a [compound SELECT] statement, only the last or right-most [simple SELECT] may have an ORDER BY clause. ^That ORDER BY clause will apply across all elements of the compound. ^If the right-most element of a [compound SELECT] is a [VALUES] clause, then no ORDER BY clause is allowed on that statement. <p>^Rows are first sorted based on the results of evaluating the left-most expression in the ORDER BY list, then ties are broken by evaluating the second left-most expression and so on. The order in which two rows for which all ORDER BY expressions evaluate to equal values are returned is undefined. ^Each ORDER BY expression may be optionally followed by one of the keywords ASC (smaller values are returned first) or DESC (larger values are returned first). ^If neither ASC or DESC are specified, rows are sorted in ascending (smaller values first) order by default. <tcl>hd_fragment nullslast {NULLS FIRST} {NULLS LAST}</tcl> <p>SQLite considers NULL values to be smaller than any other values for sorting purposes. Hence, NULLs naturally appear at the beginning of an ASC order-by and at the end of a DESC order-by. This can be changed using the "ASC NULLS LAST" or "DESC NULLS FIRST" syntax. <p>Each ORDER BY expression is processed as follows:</p> <ol> <li><p>^If the ORDER BY expression is a constant integer K then the expression is considered an alias for the K-th column of the result set (columns are numbered from left to right starting with 1). <li><p>^If the ORDER BY expression is an identifier that corresponds to the alias of one of the output columns, then the expression is considered an alias for that column. <li><p>^Otherwise, if the ORDER BY expression is any other expression, it is evaluated and the returned value used to order the output rows. ^If the SELECT statement is a simple SELECT, then an ORDER BY may contain any arbitrary expressions. ^However, if the SELECT is a compound SELECT, then ORDER BY expressions that are not aliases to output columns must be exactly the same as an expression used as an output column. </ol> <p>^For the purposes of sorting rows, values are compared in the same way as for [comparison expressions]. The collation sequence used to compare two text values is determined as follows: <ol> <li><p>^If the ORDER BY expression is assigned a collation sequence using the postfix [COLLATE operator], then the specified collation sequence is used. <li><p>^Otherwise, if the ORDER BY expression is an alias to an expression that has been assigned a collation sequence using the postfix [COLLATE operator], then the collation sequence assigned to the aliased expression is used. <li><p>^Otherwise, if the ORDER BY expression is a column or an alias of an expression that is a column, then the default collation sequence for the column is used. <li><p>^Otherwise, the [BINARY] collation sequence is used. </ol> <p>In a [compound SELECT] statement, all ORDER BY expressions are handled as aliases for one of the result columns of the compound. ^(If an ORDER BY expression is not an integer alias, then SQLite searches the left-most SELECT in the compound for a result column that matches either the second or third rules above. If a match is found, the search stops and the expression is handled as an alias for the result column that it has been matched against. Otherwise, the next SELECT to the right is tried, and so on.)^ ^If no matching expression can be found in the result columns of any constituent SELECT, it is an error. ^Each term of the ORDER BY clause is processed separately and may be matched against result columns from different SELECT statements in the compound.</p> <tcl>hd_fragment limitoffset {LIMIT} {OFFSET}</tcl> <h1>The LIMIT clause</h1> <p>^The LIMIT clause is used to place an upper bound on the number of rows returned by the entire SELECT statement. <p>^In a [compound SELECT], only the last or right-most [simple SELECT] may contain a LIMIT clause. ^In a [compound SELECT], the LIMIT clause applies to the entire compound, not just the final SELECT. ^If the right-most [simple SELECT] is a [VALUES clause] then no LIMIT clause is allowed. <p>^Any scalar expression may be used in the LIMIT clause, so long as it evaluates to an integer or a value that can be losslessly converted to an integer. ^If the expression evaluates to a NULL value or any other value that cannot be losslessly converted to an integer, an error is returned. ^If the LIMIT expression evaluates to a negative value, then there is no upper bound on the number of rows returned. ^Otherwise, the SELECT returns the first N rows of its result set only, where N is the value that the LIMIT expression evaluates to. ^Or, if the SELECT statement would return less than N rows without a LIMIT clause, then the entire result set is returned. <p>^The expression attached to the optional OFFSET clause that may follow a LIMIT clause must also evaluate to an integer, or a value that can be losslessly converted to an integer. ^If an expression has an OFFSET clause, then the first M rows are omitted from the result set returned by the SELECT statement and the next N rows are returned, where M and N are the values that the OFFSET and LIMIT clauses evaluate to, respectively. ^Or, if the SELECT would return less than M+N rows if it did not have a LIMIT clause, then the first M rows are skipped and the remaining rows (if any) are returned. ^If the OFFSET clause evaluates to a negative value, the results are the same as if it had evaluated to zero. <p>^Instead of a separate OFFSET clause, the LIMIT clause may specify two scalar expressions separated by a comma. ^In this case, the first expression is used as the OFFSET expression and the second as the LIMIT expression. This is counter-intuitive, as when using the OFFSET clause the second of the two expressions is the OFFSET and the first the LIMIT. This reversal of the offset and limit is intentional - it maximizes compatibility with other SQL database systems. However, to avoid confusion, programmers are strongly encouraged to use the form of the LIMIT clause that uses the "OFFSET" keyword and avoid using a LIMIT clause with a comma-separated offset. <tcl>hd_fragment values {VALUES clause} VALUES</tcl> <h1>The VALUES clause</h1> <p>^(The phrase "VALUES(<i>expr-list</i>)" means the same thing as "SELECT <i>expr-list</i>".)^ ^(The phrase "VALUES(<i>expr-list-1</i>),...,(<i>expr-list-N</i>)" means the same thing as "SELECT <i>expr-list-1</i> UNION ALL ... UNION ALL SELECT <i>expr-list-N</i>".)^ Both forms are the same, except that the number of SELECT statements in a compound is limited by [SQLITE_LIMIT_COMPOUND_SELECT] whereas the number of rows in a VALUES clause has no arbitrary limit. <p>There are some restrictions on the use of a VALUES clause that are not shown on the syntax diagrams: <ul> <li><p> ^A VALUES clause cannot be followed by [ORDER BY]. <li><p> ^A VALUES clause cannot be followed by [LIMIT]. </ul> <h1>The WITH Clause</h1> <p>^SELECT statements may be optionally preceded by a single [WITH clause] that defines one or more [common table expressions] for use within the SELECT statement. <tcl>hd_fragment tabfunc1 {table-valued functions in the FROM clause}</tcl> <h1>Table-valued Functions In The FROM Clause</h1> <p>A [virtual table] that contains [hidden columns] can be used like a [table-valued function] in the FROM clause. The arguments to the table-valued function become constraints on the HIDDEN columns of the virtual table. Additional information can be found in the [table-valued functions|virtual table documentation]. |
Added pages/lang_update.in.
> > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > | 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60 61 62 63 64 65 66 67 68 69 70 71 72 73 74 75 76 77 78 79 80 81 82 83 84 85 86 87 88 89 90 91 92 93 94 95 96 97 98 99 100 101 102 | <title>UPDATE</title> <tcl> hd_keywords *langupdate UPDATE *UPDATEs </tcl> <table_of_contents> <h1>Overview</h1> <tcl> RecursiveBubbleDiagram update-stmt </tcl> <p>^An UPDATE statement is used to modify a subset of the values stored in zero or more rows of the database table identified by the [qualified-table-name] specified as part of the UPDATE statement. <h1>Details</h1> <p>^If the UPDATE statement does not have a WHERE clause, all rows in the table are modified by the UPDATE. ^Otherwise, the UPDATE affects only those rows for which the WHERE clause [boolean expression|boolean expression is true]. ^It is not an error if the WHERE clause does not evaluate to true for any row in the table - this just means that the UPDATE statement affects zero rows. <p>The modifications made to each row affected by an UPDATE statement are determined by the list of assignments following the SET keyword. Each assignment specifies a <yyterm>column-name</yyterm> to the left of the equals sign and a scalar expression to the right. ^For each affected row, the named columns are set to the values found by evaluating the corresponding scalar expressions. ^If a single column-name appears more than once in the list of assignment expressions, all but the rightmost occurrence is ignored. ^Columns that do not appear in the list of assignments are left unmodified. ^The scalar expressions may refer to columns of the row being updated. ^In this case all scalar expressions are evaluated before any assignments are made. <p>Beginning in SQLite [version 3.15.0] ([dateof:3.15.0]), an assignment in the SET clause can be a [column-name-list|parenthesized list of column names] on the left and a [row value] of the same size on the right. <p>^The optional "OR <i>action</i>" conflict clause that follows the UPDATE keyword allows the user to nominate a specific constraint conflict resolution algorithm to use during this one UPDATE command. Refer to the section entitled [ON CONFLICT] for additional information. <h2>Restrictions on UPDATE Statements Within CREATE TRIGGER</h2> <p>The following additional syntax restrictions apply to UPDATE statements that occur within the body of a [CREATE TRIGGER] statement. <ul> <li><p>^The <yyterm>table-name</yyterm> specified as part of an UPDATE statement within a trigger body must be unqualified. ^(In other words, the <i>schema-name</i><b>.</b> prefix on the table name of the UPDATE is not allowed within triggers.)^ ^Unless the table to which the trigger is attached is in the TEMP database, the table being updated by the trigger program must reside in the same database as it. ^If the table to which the trigger is attached is in the TEMP database, then the unqualified name of the table being updated is resolved in the same way as it is for a top-level statement (by searching first the TEMP database, then the main database, then any other databases in the order they were attached). <li><p>^The INDEXED BY and NOT INDEXED clauses are not allowed on UPDATE statements within triggers.</p> <li><p>^The LIMIT and ORDER BY clauses for UPDATE are unsupported within triggers, regardless of the compilation options used to build SQLite. </ul> <h2>Optional LIMIT and ORDER BY Clauses</h2> <p>^(If SQLite is built with the [SQLITE_ENABLE_UPDATE_DELETE_LIMIT] compile-time option then the syntax of the UPDATE statement is extended with optional ORDER BY and LIMIT clauses)^ as follows:</p> <tcl>BubbleDiagram update-stmt-limited</tcl> <p>^If an UPDATE statement has a LIMIT clause, the maximum number of rows that will be updated is found by evaluating the accompanying expression and casting it to an integer value. ^A negative value is interpreted as "no limit". <p>^If the LIMIT expression evaluates to non-negative value <i>N</i> and the UPDATE statement has an ORDER BY clause, then all rows that would be updated in the absence of the LIMIT clause are sorted according to the ORDER BY and the first <i>N</i> updated. ^(If the UPDATE statement also has an OFFSET clause, then it is similarly evaluated and cast to an integer value. If the OFFSET expression evaluates to a non-negative value <i>M</i>, then the first <i>M</i> rows are skipped and the following <i>N</i> rows updated instead.)^ <p>^If the UPDATE statement has no ORDER BY clause, then all rows that would be updated in the absence of the LIMIT clause are assembled in an arbitrary order before applying the LIMIT and OFFSET clauses to determine which are actually updated. <p>^(The ORDER BY clause on an UPDATE statement is used only to determine which rows fall within the LIMIT. The order in which rows are modified is arbitrary and is not influenced by the ORDER BY clause.)^ |
Added pages/lang_upsert.in.
> > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > | 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60 61 62 63 64 65 66 67 68 69 70 71 72 73 74 75 76 77 78 79 80 81 82 83 84 85 86 87 88 89 90 91 92 93 94 95 96 97 98 99 100 101 102 103 104 105 106 107 108 109 110 111 112 113 114 115 116 117 118 119 120 121 122 123 124 125 126 127 128 129 130 131 132 | <title>UPSERT</title> <tcl> hd_keywords *upsert UPSERT {upsert clause} </tcl> <fancy_format> <h1>Syntax</h1> <tcl> RecursiveBubbleDiagram upsert-clause </tcl> <h1>Description</h1> <p>UPSERT is a special syntax addition to [INSERT] that causes the INSERT to behave as an [UPDATE] or a no-op if the INSERT would violate a uniqueness constraint. UPSERT is not standard SQL. UPSERT in SQLite follows the syntax established by PostgreSQL. UPSERT syntax was added to SQLite with version 3.24.0 ([dateof:3.24.0]). <p>An UPSERT is an ordinary [INSERT] statement that is followed by the special ON CONFLICT clause shown above. <p>The syntax that occurs in between the "ON CONFLICT" and "DO" keywords is called the "conflict target". The conflict target specifies a specific uniqueness constraint that will trigger the upsert. The conflict target is required for DO UPDATE upserts, but is optional for DO NOTHING. When the conflict target is omitted, the upsert behavior is triggered by a violation of any uniqueness constraint on the table of the INSERT. <p>If the insert operation would cause the uniqueness constraint identified by the conflict-target clause to fail, then the insert is omitted and either the DO NOTHING or DO UPDATE operation is performed instead. In the case of a multi-row insert, this decision is made separately for each row of the insert. <p>The special UPSERT processing happens only for uniqueness constraint on the table that is receiving the INSERT. A "uniqueness constraint" is an explicit UNIQUE or PRIMARY KEY constraint within the CREATE TABLE statement, or a [unique index]. UPSERT does not intervene for failed NOT NULL or foreign key constraints or for constraints that are implemented using triggers. <p>Column names in the expressions of a DO UPDATE refer to the original unchanged value of the column, before the attempted INSERT. To use the value that would have been inserted had the constraint not failed, add the special "excluded." table qualifier to the column name. <p>Some examples will help illustrate the difference: <blockquote><pre> CREATE TABLE vocabulary(word TEXT PRIMARY KEY, count INT DEFAULT 1); INSERT INTO vocabulary(word) VALUES('jovial') ON CONFLICT(word) DO UPDATE SET count=count+1; </pre></blockquote> <p>The upsert above inserts the new vocabulary word "jovial" if that word is not already in the dictionary, or if it is already in the dictionary, it increments the counter. The "count+1" expression could also be written as "vocabulary.count". PostgreSQL requires the second form, but SQLite accepts either. <blockquote><pre> CREATE TABLE phonebook(name TEXT PRIMARY KEY, phonenumber TEXT); INSERT INTO phonebook(name,phonenumber) VALUES('Alice','704-555-1212') ON CONFLICT(name) DO UPDATE SET phonenumber=excluded.phonenumber; </pre></blockquote> <p>In the second example, the expression in the DO UPDATE clause is of the form "excluded.phonenumber". The "excluded." prefix causes the "phonenumber" to refer to the value for phonenumber that would have been inserted had there been no conflict. Hence, the effect of the upsert is to insert a phonenumber of Alice if none exists, or to overwrite any prior phonenumber for Alice with the new one. <p>Note that the DO UPDATE clause acts only on the single row that experienced the constraint error during INSERT. It is not necessary to include a WHERE clause that restrictions the action to that one row. The only use for the WHERE clause at the end of the DO UPDATE is to optionally change the DO UPDATE into a no-op depending on the original and/or new values. For example: <blockquote><pre> CREATE TABLE phonebook2( name TEXT PRIMARY KEY, phonenumber TEXT, validDate DATE ); INSERT INTO phonebook2(name,phonenumber,validDate) VALUES('Alice','704-555-1212','2018-05-08') ON CONFLICT(name) DO UPDATE SET phonenumber=excluded.phonenumber, validDate=excluded.validDate WHERE excluded.validDate>phonebook2.validDate; </pre></blockquote> <p>In this last example, the phonebook2 entry is only updated if the validDate for the newly inserted value is newer than the entry already in the table. If the table already contains an entry with the same name and a current validDate, then the WHERE clause causes the DO UPDATE to become a no-op. <tcl>hd_fragment parseambig {UPSERT parsing ambiguity}</tcl> <h2>Parsing Ambiguity</h2> <p>When the [INSERT] statement to which the UPSERT is attached takes its values from a [SELECT] statement, there is a potential parsing ambiguity. The parser might not be able to tell if the "ON" keyword is introducing the UPSERT or if it is the ON clause of a join. To work around this, the SELECT statement should always include a WHERE clause, even if that WHERE clause is just "WHERE true". <p>Ambiguous use of ON: <blockquote><pre> INSERT INTO t1 SELECT * FROM t2 ON CONFLICT(x) DO UPDATE SET y=excluded.y; </pre></blockquote> <p>Ambiguity resolved using a WHERE clause: <blockquote><pre> INSERT INTO t1 SELECT * FROM t2 <font color="blue">WHERE true</font> ON CONFLICT(x) DO UPDATE SET y=excluded.y; </pre></blockquote> <h1>Limitations</h1> <p>UPSERT does not currently work for [virtual tables]. |
Added pages/lang_vacuum.in.
> > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > | 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60 61 62 63 64 65 66 67 68 69 70 71 72 73 74 75 76 77 78 79 80 81 82 83 84 85 86 87 88 89 90 91 92 93 94 95 96 97 98 99 100 101 102 103 104 105 106 107 108 109 110 111 112 113 114 115 116 117 118 119 120 121 122 123 124 125 126 127 128 129 130 131 132 133 134 135 136 137 138 139 140 141 142 143 144 | <title>VACUUM</title> <tcl> hd_keywords *langvacuum vacuum VACUUM </tcl> <fancy_format> <h1>Syntax</h1> <tcl> RecursiveBubbleDiagram vacuum-stmt </tcl> <h1>Description</h1> <p> The VACUUM command rebuilds the database file, repacking it into a minimal amount of disk space. There are several reasons an application might do this: <ul> <li> <p> ^Unless SQLite is running in "auto_vacuum=FULL" mode, when a large amount of data is deleted from the database file it leaves behind empty space, or "free" database pages. This means the database file might be larger than strictly necessary. ^Running VACUUM to rebuild the database reclaims this space and reduces the size of the database file. <li> <p> ^Frequent inserts, updates, and deletes can cause the database file to become fragmented - where data for a single table or index is scattered around the database file. ^Running VACUUM ensures that each table and index is largely stored contiguously within the database file. ^In some cases, VACUUM may also reduce the number of partially filled pages in the database, reducing the size of the database file further. <li> <p> When content is deleted from an SQLite database, the content is not usually erased but rather the space used to hold the content is marked as being available for reuse. This can allow deleted content to be recovered by a hacker or by forensic analysis. Running VACUUM will clean the database of all traces of deleted content, thus preventing an adversary from recovering deleted content. Using VACUUM in this way is an alternative to setting [PRAGMA secure_delete=ON]. <li> <p> ^Normally, the database [page_size] and whether or not the database supports [auto_vacuum] must be configured before the database file is actually created. ^However, when not in [write-ahead log] mode, the [page_size] and/or [auto_vacuum] properties of an existing database may be changed by using the [page_size pragma|page_size] and/or [auto_vacuum|pragma auto_vacuum] pragmas and then immediately VACUUMing the database. ^When in [write-ahead log] mode, only the [auto_vacuum] support property can be changed using VACUUM. </ul> <p>^By default, VACUUM only works only on the main database. ^[ATTACH|Attached databases] can be vacuumed by appending the appropriate <yyterm>schema-name</yyterm> to the VACUUM statement. <p><b>Compatibility Warning:</b> The ability to vacuum attached databases was added in [version 3.15.0] ([dateof:3.15.0]). Prior to that, a <yyterm>schema-name</yyterm> added to the VACUUM statement would be silently ignored and the "main" schema would be vacuumed.</p> <tcl>hd_fragment vacuuminto {VACUUM INTO}</tcl> <h2>VACUUM with an INTO clause</h2> <p>^If the INTO clause is included, then the original database file is unchanged and a new database is created in the filename given by the argument to the INTO clause. The new database will contain the same logical content as the original database, fully vacuumed. <p> The VACUUM command with an INTO clause is an alternative to the [backup API] for generating backup copies of a live database. The advantage of using VACUUM INTO is that the resulting backup database is minimal in size and hence the amount of filesystem I/O may be reduced. Also, all deleted content is purged from the backup, leaving behind no forensic traces. On the other hand, the [backup API] uses fewer CPU cycles and can be executed incrementally. <p> ^The filename in the INTO clause can be an arbitrary SQL expression that evaluates to a string. ^The file named by the INTO clause must not previously exist, or else it must be an empty file, or the VACUUM INTO command will fail with an error. <p> ^The argument to INTO can be a [URI filename] if URI filenames are enabled. URL filenames are enabled if any of the following are true: <ul> <li> The SQLite library was compiled with [-DSQLITE_USE_URI=1]. <li> The [sqlite3_config]([SQLITE_CONFIG_URI],1) interfaces was invoked at start-time. <li> The [database connection] that is running the VACUUM INTO statement was originally opened using the [SQLITE_OPEN_URI] flag. </ul> <p> The VACUUM INTO command is transactional in the sense that the generated output database is a consistent snapshot of the original database. However, if the VACUUM INTO command is interrupted by an unplanned shutdown or power lose, then the generated output database might be incomplete and corrupt. Also, SQLite does not invoke fsync() or FlushFileBuffers() on the generated database to ensure that it has reached non-volatile storage before completing. <tcl>hd_fragment howvacuumworks {how vacuum works}</tcl> <h1>How VACUUM works</h1> <p>^The VACUUM command works by copying the contents of the database into a temporary database file and then overwriting the original with the contents of the temporary file. ^When overwriting the original, a rollback journal or [write-ahead log] WAL file is used just as it would be for any other database transaction. ^This means that when VACUUMing a database, as much as twice the size of the original database file is required in free disk space. <p>^The VACUUM INTO command works the same way except that it uses the file named on the INTO clause in place of the temporary database and omits the step of copying the vacuumed database back over top of the original database. <p>^The VACUUM command may change the [ROWID | ROWIDs] of entries in any tables that do not have an explicit [INTEGER PRIMARY KEY]. </p> <p>^A VACUUM will fail if there is an open transaction on the database connection that is attempting to run the VACUUM. ^Unfinalized SQL statements typically hold a read transaction open, so the VACUUM might fail if there are unfinalized SQL statements on the same connection. ^VACUUM (but not VACUUM INTO) is a write operation and so if another database connection is holding a lock that prevents writes, then the VACUUM will fail. <p>^(An alternative to using the VACUUM command to reclaim space after data has been deleted is auto-vacuum mode, enabled using the [auto_vacuum] pragma.)^ ^When [auto_vacuum] is enabled for a database free pages may be reclaimed after deleting data, causing the file to shrink, without rebuilding the entire database using VACUUM. ^However, using [auto_vacuum] can lead to extra database file fragmentation. ^And [auto_vacuum] does not compact partially filled pages of the database as VACUUM does. </p> |
Added pages/lang_with.in.
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There are two kinds of common table expressions: "ordinary" and "recursive". Ordinary common table expressions are helpful for making queries easier to understand by factoring subqueries out of the main SQL statement. Recursive common table expressions provide the ability to do hierarchical or recursive queries of trees and graphs, a capability that is not otherwise available in the SQL language. <p>All common table expressions (ordinary and recursive) are created by prepending a WITH clause in front of a [SELECT], [INSERT], [DELETE], or [UPDATE] statement. A single WITH clause can specify one or more common table expressions, some of which are ordinary and some of which are recursive. <tcl>hd_fragment ordinarycte {ordinary common table expressions}</tcl> <h1>Ordinary Common Table Expressions</h1> <p>An ordinary common table expression works as if it were a [view] that exists for the duration of a single statement. Ordinary common table expressions are useful for factoring out subqueries and making the overall SQL statement easier to read and understand. <p>A WITH clause can contain ordinary common table expressions even if it includes the RECURSIVE keyword. The use of RECURSIVE does not force common table expressions to be recursive. <tcl> hd_fragment recursivecte {recursive common table expressions} \ {recursive common table expression} {recursive query} </tcl> <h1>Recursive Common Table Expressions</h1> <p>A recursive common table expression can be used to write a query that walks a tree or graph. A recursive common table expression has the same basic syntax as an ordinary common table expression, but with the following additional features: <ol> <li> The "[select-stmt]" must be a [compound select] where the right-most [compound-operator] is either UNION or UNION ALL. <li> The table named on the left-hand side of the AS keyword must appear exactly once in the FROM clause of the right-most SELECT statement of the compound select, and nowhere else. <li> The right-most SELECT of the compound select must not make use of [Aggregate Functions|aggregate] or [window functions]. </ol> <p>To put it another way, a recursive common table expression must look like the following: <tcl>RecursiveBubbleDiagram recursive-cte</tcl> <p>Call the table named by the [cte-table-name] in a recursive common table expression the "recursive table". In the [recursive-cte] bubble diagram above, the recursive table must appear exactly once in the FROM clause of the <yyterm>recursive-select</yyterm> and must not appear anywhere else in either the <yyterm>initial-select</yyterm> or the <yyterm>recursive-select</yyterm>, including subqueries. The <yyterm>initial-select</yyterm> may be a [compound select], but it may not include an ORDER BY, LIMIT, or OFFSET. The recursive-select must be a simple select, not a compound. The recursive-select is allowed to include an ORDER BY, LIMIT, and/or OFFSET. <p>The basic algorithm for computing the content of the recursive table is as follows: <ol> <li> Run the <yyterm>initial-select</yyterm> and add the results to a queue. <li> While the queue is not empty: <ol type="a"> <li> Extract a single row from the queue. <li> Insert that single row into the recursive table <li> Pretend that the single row just extracted is the only row in the recursive table and run the recursive-select, adding all results to the queue. </ol> </ol> <p>The basic procedure above may modified by the following additional rules: <ul> <li><p> If a UNION operator connects the <yyterm>initial-select</yyterm> with the <yyterm>recursive-select</yyterm>, then only add rows to the queue if no identical row has been previously added to the queue. Repeated rows are discarded before being added to the queue even if the repeated rows have already been extracted from the queue by the recursion step. If the operator is UNION ALL, then all rows generated by both the <yyterm>initial-select</yyterm> and the <yyterm>recursive-select</yyterm> are always added to the queue even if they are repeats. When determining if a row is repeated, NULL values compare equal to one another and not equal to any other value. <li><p> The LIMIT clause, if present, determines the maximum number of rows that will ever be added to the recursive table in step 2b. Once the limit is reached, the recursion stops. A limit of zero means that no rows are ever added to the recursive table, and a negative limit means an unlimited number of rows may be added to the recursive table. <li><p> The OFFSET clause, if it is present and has a positive value N, prevents the first N rows from being added to the recursive table. The first N rows are still processed by the <yyterm>recursive-select</yyterm> — they just are not added to the recursive table. Rows are not counted toward fulfilling the LIMIT until all OFFSET rows have been skipped. <li><p> If an ORDER BY clause is present, it determines the order in which rows are extracted from the queue in step 2a. If there is no ORDER BY clause, then the order in which rows are extracted is undefined. (In the current implementation, the queue becomes a FIFO if the ORDER BY clause is omitted, but applications should not depend on that fact since it might change.) </ul> <tcl>hd_fragment rcex1</tcl> <h2>Recursive Query Examples</h2> <p>The following query returns all integers between 1 and 1000000: <blockquote><pre> WITH RECURSIVE cnt(x) AS (VALUES(1) UNION ALL SELECT x+1 FROM cnt WHERE x<1000000) SELECT x FROM cnt; </pre></blockquote> <p>Consider how this query works. The initial-select runs first and returns a single row with a single column "1". This one row is added to the queue. In step 2a, that one row is extracted from the queue and added to "cnt". Then the recursive-select is run in accordance with step 2c generating a single new row with value "2" to add to the queue. The queue still has one row, so step 2 repeats. The "2" row is extracted and added to the recursive table by steps 2a and 2b. Then the row containing 2 is used as if it were the complete content of the recursive table and the recursive-select is run again, resulting in a row with value "3" being added to the queue. This repeats 999999 times until finally at step 2a the only value on the queue is a row containing 1000000. That row is extracted and added to the recursive table. But this time, the WHERE clause causes the recursive-select to return no rows, so the queue remains empty and the recursion stops. <p><b>Optimization note:</b> In the discussion above, statements like "insert the row into the recursive table" should be understood conceptually, not literally. It sounds as if SQLite is accumulating a huge table containing one million rows, then going back and scanning that table from top to bottom to generate the result. What really happens is that the query optimizer sees that values in the "cnt" recursive table are only used once. So as each row is added to the recursive table, that row is immediately returned as a result of the main SELECT statement and then discarded. SQLite does <em>not</em> accumulate a temporary table containing a million rows. Very little memory is needed to run the above example. However, if the example had used UNION instead of UNION ALL, then SQLite would have had to keep around all previously generated content in order to check for duplicates. For this reason, programmers should strive to use UNION ALL instead of UNION when feasible. <p>Here is a variation on the previous example: <blockquote><pre> WITH RECURSIVE cnt(x) AS ( SELECT 1 UNION ALL SELECT x+1 FROM cnt LIMIT 1000000 ) SELECT x FROM cnt; </pre></blockquote> <p>There are two differences in this variation. The initial-select is "SELECT 1" instead of "VALUES(1)". But those are just different syntaxes for saying exactly the same thing. The other change is that the recursion is stopped by a LIMIT rather than a WHERE clause. The use of LIMIT means that when the one-millionth row is added to the "cnt" table (and returned by the main SELECT, thanks to the query optimizer) then the recursion stops immediately regardless of how many rows might be left in the queue. On more complex queries, it can sometimes be difficult to ensure that the WHERE clause will eventually cause the queue to drain and the recursion to terminate. But the LIMIT clause will always stop the recursion. So it is good practice to always include a LIMIT clause as a safety if an upper bound on the size of the recursion is known. <tcl>hd_fragment rcex2</tcl> <h2>Hierarchical Query Examples</h2> <p>Consider a table that describes the members of an organization as well as the chain-of-command within that organization: <blockquote><pre> CREATE TABLE org( name TEXT PRIMARY KEY, boss TEXT REFERENCES org, height INT, -- other content omitted ); </pre></blockquote> <p>Every member in the organization has a name, and most members have a single boss. (The head of the whole organization has a NULL "boss" field.) The rows of the "org" table form a tree. <p>Here is a query that computes the average height over everyone in Alice's organization, including Alice: <blockquote><pre> WITH RECURSIVE works_for_alice(n) AS ( VALUES('Alice') UNION SELECT name FROM org, works_for_alice WHERE org.boss=works_for_alice.n ) SELECT avg(height) FROM org WHERE org.name IN works_for_alice; </pre></blockquote> <p>The next example uses two common table expressions in a single WITH clause. The following table records a family tree: <blockquote><pre> CREATE TABLE family( name TEXT PRIMARY KEY, mom TEXT REFERENCES family, dad TEXT REFERENCES family, born DATETIME, died DATETIME, -- NULL if still alive -- other content ); </pre></blockquote> <p>The "family" table is similar to the earlier "org" table except that now there are two parents to each member. We want to know all living ancestors of Alice, from oldest to youngest. An ordinary common table expression, "parent_of", is defined first. That ordinary CTE is a view that can be used to find all parents of any individual. That ordinary CTE is then used in the "ancestor_of_alice" recursive CTE. The recursive CTE is then used in the final query: <blockquote><pre> WITH RECURSIVE parent_of(name, parent) AS (SELECT name, mom FROM family UNION SELECT name, dad FROM family), ancestor_of_alice(name) AS (SELECT parent FROM parent_of WHERE name='Alice' UNION ALL SELECT parent FROM parent_of JOIN ancestor_of_alice USING(name)) SELECT family.name FROM ancestor_of_alice, family WHERE ancestor_of_alice.name=family.name AND died IS NULL ORDER BY born; </pre></blockquote> <tcl>hd_fragment rcex3</tcl> <h2>Queries Against A Graph</h2> <p>A version control system (VCS) will typically store the evolving versions of a project as a directed acyclic graph (DAG). Call each version of the project a "checkin". A single checkin can have zero or more parents. Most checkins (except the first) have a single parent, but in the case of a merge, a checkin might have two or three or more parents. A schema to keep track of checkins and the order in which they occur might look something like this: <blockquote><pre> CREATE TABLE checkin( id INTEGER PRIMARY KEY, mtime INTEGER -- timestamp when this checkin occurred ); CREATE TABLE derivedfrom( xfrom INTEGER NOT NULL REFERENCES checkin, -- parent checkin xto INTEGER NOT NULL REFERENCES checkin, -- derived checkin PRIMARY KEY(xfrom,xto) ); CREATE INDEX derivedfrom_back ON derivedfrom(xto,xfrom); </pre></blockquote> <p>This graph is acyclic. And we assume that the mtime of every child checkin is no less than the mtime of all its parents. But unlike the earlier examples, this graph might have multiple paths of differing lengths between any two checkins. <p>We want to know the twenty most recent ancestors in time (out of the thousands and thousands of ancestors in the whole DAG) for checkin "@BASELINE". (A query similar to this is used by the <a href="http://www.fossil-scm.org/">Fossil</a> VCS to show the N most recent ancestors of a check. For example: <a href="http://www.sqlite.org/src/timeline?p=trunk&n=30">http://www.sqlite.org/src/timeline?p=trunk&n=30</a>.) <blockquote><pre> WITH RECURSIVE ancestor(id,mtime) AS ( SELECT id, mtime FROM checkin WHERE id=@BASELINE UNION SELECT derivedfrom.xfrom, checkin.mtime FROM ancestor, derivedfrom, checkin WHERE ancestor.id=derivedfrom.xto AND checkin.id=derivedfrom.xfrom ORDER BY checkin.mtime DESC LIMIT 20 ) SELECT * FROM checkin JOIN ancestor USING(id); </pre></blockquote> <p> The "ORDER BY checkin.mtime DESC" term in the recursive-select makes the query run much faster by preventing it from following branches that merge checkins from long ago. The ORDER BY forces the recursive-select to focus on the most recent checkins, the ones we want. Without the ORDER BY on the recursive-select, one would be forced to compute the complete set of thousands of ancestors, sort them all by mtime, then take the top twenty. The ORDER BY essentially sets up a priority queue that forces the recursive query to look at the most recent ancestors first, allowing the use of a LIMIT clause to restrict the scope of the query to just the checkins of interest. <tcl>hd_fragment withorderby</tcl> <h2>Controlling Depth-First Versus Breadth-First Search Of a Tree Using ORDER BY</h2> <p>An ORDER BY clause on the recursive-select can be used to control whether the search of a tree is depth-first or breadth-first. To illustrate, we will use a variation on the "org" table from an example above, without the "height" column, and with some real data inserted: <blockquote><pre> CREATE TABLE org( name TEXT PRIMARY KEY, boss TEXT REFERENCES org ) WITHOUT ROWID; INSERT INTO org VALUES('Alice',NULL); INSERT INTO org VALUES('Bob','Alice'); INSERT INTO org VALUES('Cindy','Alice'); INSERT INTO org VALUES('Dave','Bob'); INSERT INTO org VALUES('Emma','Bob'); INSERT INTO org VALUES('Fred','Cindy'); INSERT INTO org VALUES('Gail','Cindy'); </pre></blockquote> <p>Here is a query to show the tree structure in a breadth-first pattern: <blockquote><pre> WITH RECURSIVE under_alice(name,level) AS ( VALUES('Alice',0) UNION ALL SELECT org.name, under_alice.level+1 FROM org JOIN under_alice ON org.boss=under_alice.name ORDER BY 2 ) SELECT substr('..........',1,level*3) || name FROM under_alice; </pre></blockquote> <p>The "ORDER BY 2" (which means the same as "ORDER BY under_alice.level+1") causes higher levels in the organization chart (with smaller "level" values) to be processed first, resulting in a breadth-first search. The output is: <blockquote><pre> Alice ...Bob ...Cindy ......Dave ......Emma ......Fred ......Gail </pre></blockquote> <p>But if we change the ORDER BY clause to add the "DESC" modifier, that will cause lower levels in the organization (with larger "level" values) to be processed first by the recursive-select, resulting in a depth-first search: <blockquote><pre> WITH RECURSIVE under_alice(name,level) AS ( VALUES('Alice',0) UNION ALL SELECT org.name, under_alice.level+1 FROM org JOIN under_alice ON org.boss=under_alice.name ORDER BY 2 <b>DESC</b> ) SELECT substr('..........',1,level*3) || name FROM under_alice; </pre></blockquote> <p>The output of this revised query is: <blockquote><pre> Alice ...Bob ......Dave ......Emma ...Cindy ......Fred ......Gail </pre></blockquote> <p>When the ORDER BY clause is omitted from the recursive-select, the queue behaves as a FIFO, which results in a breadth-first search. <tcl>hd_fragment mandelbrot {compute the Mandelbrot set}</tcl> <h2>Outlandish Recursive Query Examples</h2> <p>The following query computes an approximation of the Mandelbrot Set and outputs the result as ASCII-art: <blockquote><pre> WITH RECURSIVE xaxis(x) AS (VALUES(-2.0) UNION ALL SELECT x+0.05 FROM xaxis WHERE x<1.2), yaxis(y) AS (VALUES(-1.0) UNION ALL SELECT y+0.1 FROM yaxis WHERE y<1.0), m(iter, cx, cy, x, y) AS ( SELECT 0, x, y, 0.0, 0.0 FROM xaxis, yaxis UNION ALL SELECT iter+1, cx, cy, x*x-y*y + cx, 2.0*x*y + cy FROM m WHERE (x*x + y*y) < 4.0 AND iter<28 ), m2(iter, cx, cy) AS ( SELECT max(iter), cx, cy FROM m GROUP BY cx, cy ), a(t) AS ( SELECT group_concat( substr(' .+*#', 1+min(iter/7,4), 1), '') FROM m2 GROUP BY cy ) SELECT group_concat(rtrim(t),x'0a') FROM a; </pre></blockquote> <p>In this query, the "xaxis" and "yaxis" CTEs define the grid of points for which the Mandelbrot Set will be approximated. Each row in the "m(iter,cx,cy,x,y)" CTE means that after "iter" iterations, the Mandelbrot iteration starting at cx,cy has reached point x,y. The number of iterations in this example is limited to 28 (which severely limits the resolution of the computation, but is sufficient for low-resolution ASCII-art output). The "m2(iter,cx,cy)" CTE holds the maximum number of iterations reached when starting at point cx,cy. Finally, each row in the "a(t)" CTE holds a string which is a single line of the output ASCII-art. The SELECT statement at the end just queries the "a" CTE to retrieve all lines of ASCII-art, one by one. <p>Running the query above in an SQLite [command-line shell] results in the following output: <blockquote><pre> ....# ..#*.. ..+####+. .......+####.... + ..##+*##########+.++++ .+.##################+. .............+###################+.+ ..++..#.....*#####################+. ...+#######++#######################. ....+*################################. #############################################... ....+*################################. ...+#######++#######################. ..++..#.....*#####################+. .............+###################+.+ .+.##################+. ..##+*##########+.++++ .......+####.... + ..+####+. ..#*.. ....# +. </pre></blockquote> <tcl>hd_fragment sudoku {solve Sudoku puzzles} </tcl> <p>This next query solves a Sudoku puzzle. The state of the puzzle is defined by an 81-character string formed by reading entries from the puzzle box row by row from left to right and then from top to bottom. Blank squares in the puzzle are denoted by a "." character. Thus the input string: <blockquote> 53..7....6..195....98....6.8...6...34..8.3..17...2...6.6....28....419..5....8..79 </blockquote> <p>Corresponds to a puzzle like this: <blockquote> <table border="1" cellpadding="5"> <tr><td>5<td>3<td> <td> <td>7<td> <td> <td> <td> <tr><td>6<td> <td> <td>1<td>9<td>5<td> <td> <td> <tr><td> <td>9<td>8<td> <td> <td> <td> <td>6<td> <tr><td>8<td> <td> <td> <td>6<td> <td> <td> <td>3 <tr><td>4<td> <td> <td>8<td> <td>3<td> <td> <td>1 <tr><td>7<td> <td> <td> <td>2<td> <td> <td> <td>6 <tr><td> <td>6<td> <td> <td> <td> <td>2<td>8<td> <tr><td> <td> <td> <td>4<td>1<td>9<td> <td> <td>5 <tr><td> <td> <td> <td> <td>8<td> <td> <td>7<td>9 </table> </blockquote> <p>This is the query that solves the puzzle: <blockquote><pre> WITH RECURSIVE input(sud) AS ( VALUES('53..7....6..195....98....6.8...6...34..8.3..17...2...6.6....28....419..5....8..79') ), digits(z, lp) AS ( VALUES('1', 1) UNION ALL SELECT CAST(lp+1 AS TEXT), lp+1 FROM digits WHERE lp<9 ), x(s, ind) AS ( SELECT sud, instr(sud, '.') FROM input UNION ALL SELECT substr(s, 1, ind-1) || z || substr(s, ind+1), instr( substr(s, 1, ind-1) || z || substr(s, ind+1), '.' ) FROM x, digits AS z WHERE ind>0 AND NOT EXISTS ( SELECT 1 FROM digits AS lp WHERE z.z = substr(s, ((ind-1)/9)*9 + lp, 1) OR z.z = substr(s, ((ind-1)%9) + (lp-1)*9 + 1, 1) OR z.z = substr(s, (((ind-1)/3) % 3) * 3 + ((ind-1)/27) * 27 + lp + ((lp-1) / 3) * 6, 1) ) ) SELECT s FROM x WHERE ind=0; </pre></blockquote> <p>The "input" CTE defines the input puzzle. The "digits" CTE defines a table that holds all digits between 1 and 9. The work of solving the puzzle is undertaken by the "x" CTE. An entry in x(s,ind) means that the 81-character string "s" is a valid sudoku puzzle (it has no conflicts) and that the first unknown character is at position "ind", or ind==0 if all character positions are filled in. The goal, then, is to compute entries for "x" with an "ind" of 0. <p>The solver works by adding new entries to the "x" recursive table. Given prior entries, the recursive-select tries to fill in a single new position with all values between 1 and 9 that actually work in that position. The complicated "NOT EXISTS" subquery is the magic that figures out whether or not each candidate "s" string is a valid sudoku puzzle or not. <p>The final answer is found by looking for a string with ind==0. If the original sudoku problem did not have a unique solution, then the query will return all possible solutions. If the original problem was unsolvable, then no rows will be returned. In this case, the unique answer is: <blockquote> 534678912672195348198342567859761423426853791713924856961537284287419635345286179 </blockquote> <p>The solution was computed in less than 300 milliseconds on a modern workstation. <h1>Limitations And Caveats</h1> <ul> <li><p> The WITH clause cannot be used within a [CREATE TRIGGER]. <li><p> The WITH clause must appear at the beginning of a top-level [SELECT] statement or at the beginning of a subquery. The WITH clause cannot be prepended to the second or subsequent SELECT statement of a [compound select]. <li><p> The SQL:1999 spec requires that the RECURSIVE keyword follow WITH in any WITH clause that includes a recursive common table expression. However, for compatibility with SqlServer and Oracle, SQLite does not enforce this rule. </ul> |