<title>Query Language Understood by SQLite</title>

<h2>SQL As Understood By SQLite</h2>

<p>SQLite understands most of the standard SQL
language.  But it does <a href="omitted.html">omit some features</a>
while at the same time
adding a few features of its own.  This document attempts to
describe precisely what parts of the SQL language SQLite does
and does not support.  A list of <a href="lang_keywords.html">keywords</a> is 
also provided.  The SQL language syntax is described by
<a href="syntaxdiagrams.html">syntax diagrams</a>.</p>

<p>In all of the syntax diagrams that follow, literal text is shown in
bold blue.  Non-terminal symbols are shown in italic red.  Operators
that are part of the syntactic markup itself are shown in black roman.</p>

<p>This document is just an overview of the SQL syntax implemented
by SQLite.  Many low-level productions are omitted.  For detailed information
on the language that SQLite understands, refer to the source code and
the grammar file "parse.y".</p>

<p>The following syntax documentation topics are available:</p>

<table width="100%" cellpadding="5" border="0">
<tr><td valign="top"><ul>

<tcl>
set i 0
foreach {section} [lsort -index 0 -dictionary {
  {{CREATE TABLE} createtable}
  {{CREATE VIRTUAL TABLE} createvtab}
  {{CREATE INDEX} createindex}
  {VACUUM vacuum}
  {{DROP TABLE} droptable}
  {{DROP INDEX} dropindex}
  {INSERT insert}
  {REPLACE replace}
  {DELETE delete}
  {UPDATE update}
  {SELECT select}
  {comment comment}
  {EXPLAIN explain}
  {expression expr}
  {{BEGIN TRANSACTION} transaction}
  {{COMMIT TRANSACTION} transaction}
  {{END TRANSACTION} transaction}
  {{ROLLBACK TRANSACTION} transaction}
  {PRAGMA pragma.html}
  {{ON CONFLICT clause} conflict}
  {{CREATE VIEW} createview}
  {{DROP VIEW} dropview}
  {{CREATE TRIGGER} createtrigger}
  {{DROP TRIGGER} droptrigger}
  {{ATTACH DATABASE} attach}
  {{DETACH DATABASE} detach}
  {REINDEX reindex}
  {{ALTER TABLE} altertable}
  {{ANALYZE} analyze}
  {{aggregate functions} aggfunc}
  {{core functions} corefunc}
  {{date and time functions} datefunc}
  {keywords keywords}
}] {
  foreach {s_title s_tag} $section {}
  if {$s_tag=="pragma.html"} {
    set url $s_tag
  } else {
    set url lang_$s_tag.html
  }
  hd_puts "<li><a href=\"$url\">$s_title</a></li>"
  incr i
  if {$i==11 || $i==22} {
    hd_puts "</ul></td><td valign=\"top\"><ul>"
  }
}
</tcl>
</ul></td></tr></table>

<p>The general outline of all SQL statements understood by
SQLite is as follows:</p>

<tcl>BubbleDiagram sql-stmt</tcl>

<tcl>
proc Operator {name} {
  return "<font color=\"#2c2cf0\"><big>$name</big></font>"
}
proc Nonterminal {name} {
  return "<i><font color=\"#ff3434\">$name</font></i>"
}
proc Keyword {name} {
  return "<font color=\"#2c2cf0\">$name</font>"
}
proc Example {text} {
  hd_puts "<blockquote><pre>$text</pre></blockquote>"
}

proc Section {name label keywords} {
  global DOC
  hd_close_main
  hd_open_main lang_$label.html
  hd_header "SQLite Query Language: $name" $DOC/pages/lang.in
  eval hd_keywords $keywords
  hd_puts {<a href="lang.html"><h2>SQL As Understood By SQLite</h2></a>}
  hd_puts "<h3>$name</h3>"
}

###############################################################################
Section {ALTER TABLE} altertable {{ALTER TABLE} {ALTER}}

BubbleDiagram alter-table-stmt 1
</tcl>

<p>SQLite supports a limited subset of ALTER TABLE.
The ALTER TABLE command in SQLite allows the user to rename a table
or to add a new column to an existing table. It is not possible
to rename a colum, remove a column, or add or remove constraints from a table.
</p>

<p>The RENAME TO syntax is used to rename the table identified by 
<i>&#91;database-name.&#93;table-name</i> to <i>new-table-name</i>.
This command 
cannot be used to move a table between attached databases, only to rename 
a table within the same database.</p>

<p>If the table being renamed has triggers or indices, then these remain
attached to the table after it has been renamed. However, if there are
any view definitions, or statements executed by triggers that refer to
the table being renamed, these are not automatically modified to use the new
table name. If this is required, the triggers or view definitions must be
dropped and recreated to use the new table name by hand.
</p>

<p>The ADD COLUMN syntax
is used to add a new column to an existing table.
The new column is always appended to the end of the list of existing columns.
The [column-def] rule defines the characteristics of the new column.
The new column may take any of the forms permissable in a [CREATE TABLE]
statement, with the following restrictions:
<ul>
<li>The column may not have a PRIMARY KEY or UNIQUE constraint.</li>
<li>The column may not have a default value of CURRENT_TIME, CURRENT_DATE 
    or CURRENT_TIMESTAMP.</li>
<li>If a NOT NULL constraint is specified, then the column must have a
    default value other than NULL.
</ul>

<p>The execution time of the ALTER TABLE command is independent of
the amount of data in the table.  The ALTER TABLE command runs as quickly
on a table with 10 million rows as it does on a table with 1 row.
</p>

<p>After ADD COLUMN has been run on a database, that database will not
be readable by SQLite version 3.1.3 and earlier.</p>

<tcl>
##############################################################################
Section {ANALYZE} analyze ANALYZE

BubbleDiagram analyze-stmt 1
</tcl>

<p>The ANALYZE command gathers statistics about indices and stores them
in a special tables in the database where the query optimizer can use
them to help make better index choices.
If no arguments are given, all indices in all attached databases are
analyzed.  If a database name is given as the argument, all indices
in that one database are analyzed.  If the argument is a table name,
then only indices associated with that one table are analyzed.</p>

<p>The initial implementation stores all statistics in a single
table named <b>sqlite_stat1</b>.  Future enhancements may create
additional tables with the same name pattern except with the "1"
changed to a different digit.  The [DROP TABLE] command does
not work on the <b>sqlite_stat1</b> table,
but all the content can be removed using the [DELETE] command,
which has the same effect.</p>

<tcl>
Section {ATTACH DATABASE} attach ATTACH

BubbleDiagram attach-stmt 1
</tcl>

<p>The ATTACH DATABASE statement adds another database 
file to the current database connection.  If the filename contains 
punctuation characters it must be quoted.  The names 'main' and 
'temp' refer to the main database and the database used for 
temporary tables.  These cannot be detached.  Attached databases 
are removed using the [DETACH] statement.</p>

<p>You cannot create a new table with the same name as a table in 
an attached database, but you can attach a database which contains
tables whose names are duplicates of tables in the main database.  It is 
also permissible to attach the same database file multiple times.</p>

<p>Tables in an attached database can be referred to using the syntax 
<i>database-name.table-name</i>.  If an attached table doesn't have 
a duplicate table name in the main database, it doesn't require a 
database name prefix.  When a database is attached, all of its 
tables which don't have duplicate names become the default table
of that name.  Any tables of that name attached afterwards require the
database prefix. If the default table of a given name is detached, then
the last table of that name attached becomes the new default.</p>

<p>
Transactions involving multiple attached databases are atomic,
assuming that the main database is not ":memory:".  If the main
database is ":memory:" then 
transactions continue to be atomic within each individual
database file. But if the host computer crashes in the middle
of a [COMMIT] where two or more database files are updated,
some of those files might get the changes where others
might not.
</p>

<p>There is a compile-time limit of [SQLITE_MAX_ATTACHED]
attached database files.</p>

<tcl>
###############################################################################
Section {BEGIN TRANSACTION} transaction {BEGIN COMMIT ROLLBACK}

BubbleDiagram begin-stmt
BubbleDiagram commit-stmt
BubbleDiagram rollback-stmt
</tcl>

<p>
No changes can be made to the database except within a transaction.
Any command that changes the database (basically, any SQL command
other than [SELECT]) will automatically start a transaction if
one is not already in effect.  Automatically started transactions
are committed at the conclusion of the command.
</p>

<p>
Transactions can be started manually using the BEGIN
command.  Such transactions usually persist until the next
COMMIT or ROLLBACK command.  But a transaction will also 
ROLLBACK if the database is closed or if an error occurs
and the ROLLBACK conflict resolution algorithm is specified.
See the documentation on the [ON CONFLICT]
clause for additional information about the ROLLBACK
conflict resolution algorithm.
</p>

<p>
END TRANSACTION is an alias for COMMIT.
</p>

<p>The optional transaction name is ignored. SQLite 
does not recognize nested transactions at this time.
However, future versions of SQLite may be enhanced to support nested
transactions and the transaction name would then become significant.
Application are advised not to use the transaction name in order
to avoid future compatibility problems.</p>

<p>
Transactions can be deferred, immediate, or exclusive.  
The default transaction behavior is deferred.
Deferred means that no locks are acquired
on the database until the database is first accessed.  Thus with a
deferred transaction, the BEGIN statement itself does nothing.  Locks
are not acquired until the first read or write operation.  The first read
operation against a database creates a [SHARED] lock and the first
write operation creates a [RESERVED] lock.   Because the acquisition of
locks is deferred until they are needed, it is possible that another
thread or process could create a separate transaction and write to
the database after the BEGIN on the current thread has executed.
If the transaction is immediate, then [RESERVED] locks
are acquired on all databases as soon as the BEGIN command is
executed, without waiting for the
database to be used.  After a BEGIN IMMEDIATE, you are guaranteed that
no other thread or process will be able to write to the database or
do a BEGIN IMMEDIATE or BEGIN EXCLUSIVE.  Other processes can continue
to read from the database, however.  An exclusive transaction causes
[EXCLUSIVE] locks to be acquired on all databases.  After a BEGIN
EXCLUSIVE, you are guaranteed that no other thread or process will
be able to read or write the database until the transaction is
complete.
</p>

<p>
The COMMIT command does not actually perform a commit until all
pending SQL commands finish.  Thus if one or more [SELECT] statements
are in the middle of processing and a COMMIT is executed, the commit
will not actually occur until all [SELECT] statements have been
[sqlite3_reset() | reset] or [sqlite3_finalize() | finalized].
</p>

<p>
An attempt to execute COMMIT might result in an [SQLITE_BUSY] return code.
This indicates that another thread or process had a 
[shared lock] on the database
that prevented the database from being updated.  When COMMIT fails in this
way, the transaction remains active and the COMMIT can be retried later
after the reader has had a chance to clear.
</p>

<h3>Response To Errors Within A Transaction</h3>

<p>If certain kinds of errors occur within a transaction, the
transaction may or may not be rolled back automatically.  The
errors that cause the behavior include:</p>

<ul>
<li> [SQLITE_FULL]: database or disk full
<li> [SQLITE_IOERR]: disk I/O error
<li> [SQLITE_BUSY]: database in use by another process
<li> [SQLITE_NOMEM]: out or memory
<li> [SQLITE_INTERRUPT]: processing [sqlite3_interrupt|interrupted]
     by application request
</ul>

<p>
For all of these errors, SQLite attempts to undo just the one statement
it was working on and leave changes from prior statements within the
same transaction intact and continue with the transaction.  However, 
depending on the statement being evaluated and the point at which the
error occurs, it might be necessary for SQLite to rollback and
cancel the transaction.  An application can tell which
course of action SQLite took by using the
[sqlite3_get_autocommit()] C-language interface.</p>

<p>It is recommended that applications respond to the errors
listed above by explicitly issuing a ROLLBACK command.  If the 
transaction has already been rolled back automatically
by the error response, then the ROLLBACK command will fail with an
error, but no harm is caused by this.</p>

<p>Future versions of SQLite may extend the list of errors which
might cause automatic transaction rollback.  Future versions of
SQLite might change the error response.  In particular, we may
choose to simplify the interface in future versions of SQLite by
causing the errors above to force an unconditional rollback.</p>

<tcl>
###############################################################################
Section comment comment {comment comments}

BubbleDiagram comment-syntax
</tcl>

<p>Comments aren't SQL commands, but can occur within the text of
SQL queries passed to [sqlite3_prepare_v2()] and related interfaces..
Comments are 
treated as whitespace by the parser.  They can begin anywhere whitespace 
can be found, including inside expressions that span multiple lines.
</p>

<p> SQL comments begin with two consecutive "-" characters (ASCII 0x2d)
and extend up to and including the next newline character (ASCII 0x0a)
or until the end of input, whichever comes first.</p>

<p> C comments can span any number of lines.  C-style comments begin
with "/*" and extend up to and including the next "*/" character pair
or until the end of input, whichever comes first.  C-style comments
can span multiple lines. </p>

<p> Comments can appear anywhere whitespace can occur,
including inside expressions and in the middle of other SQL statements.
Comments do not nest.
</p>


<tcl>
##############################################################################
Section {CREATE INDEX} createindex {{CREATE INDEX}}

BubbleDiagram create-index-stmt 1
BubbleDiagram indexed-column
</tcl>

<p>The CREATE INDEX command consists of the keywords "CREATE INDEX" followed
by the name of the new index, the keyword "ON", the name of a previously
created table that is to be indexed, and a parenthesized list of names of
columns in the table that are used for the index key.</p>

<p>Each column name can be followed by one of the "ASC" or "DESC" keywords
to indicate sort order.  The sort order may or may not be ignored depending
on the database file format.  The "legacy" file format ignores index
sort order.  The descending index file format takes index sort order
into account.  Only copies of SQLite newer than [version 3.3.0] 
(released on 2006-01-10) are able to understand the newer descending
index file format and so for compatibility with older versions of
SQLite, the legacy file format is generated by default.  Use the
[legacy_file_format] pragma to modify this behavior and generate
databases that use the newer file format.  Future versions of SQLite
may begin to generate the newer file format by default.</p>

<p>The COLLATE clause following each column name defines a collating
sequence used for text entires in that column.  The default collating
sequence is the collating sequence defined for that column in the
[CREATE TABLE] statement.  Or if no collating sequence is otherwise defined,
the built-in BINARY collating sequence is used.</p>

<p>There are no arbitrary limits on the number of indices that can be
attached to a single table.  The number of columns in an index is 
limited to [SQLITE_MAX_COLUMN].</p>

<p>If the UNIQUE keyword appears between CREATE and INDEX then duplicate
index entries are not allowed.  Any attempt to insert a duplicate entry
will result in an error.  For the purposes of unique indices, all NULL values
are considered to different from all other NULL values and are thus unique.</p>

<p>The text
of each CREATE INDEX statement is stored in the <b>sqlite_master</b>
or <b>sqlite_temp_master</b> table, depending on whether the table
being indexed is temporary.  Every time the database is opened,
all CREATE INDEX statements
are read from the <b>sqlite_master</b> table and used to regenerate
SQLite's internal representation of the index layout.</p>

<p>If the optional IF NOT EXISTS clause is present and another index
with the same name aleady exists, then this command becomes a no-op.</p>

<p>Indexes are removed with the <a href="lang_dropindex.html">DROP INDEX</a> 
command.</p>


<tcl>
##############################################################################
Section {CREATE TABLE} {createtable} {{CREATE TABLE}}

BubbleDiagram create-table-stmt 1
BubbleDiagram column-def
BubbleDiagram type-name
BubbleDiagram column-constraint
BubbleDiagram table-constraint
BubbleDiagram foreign-key-clause
</tcl>

<p>A CREATE TABLE statement is basically the keywords "CREATE TABLE"
followed by the name of a new table and a parenthesized list of column
definitions and constraints.  
Tables names that begin with "<b>sqlite_</b>" are reserved
for use by the engine.</p>

<p>Each column definition is the name of the column followed by the
datatype for that column, then one or more optional column constraints.
The datatype for the column does not restrict what data may be put
in that column.
See <a href="datatype3.html">Datatypes In SQLite Version 3</a> for
additional information.
The UNIQUE constraint causes an unique index to be created on the specified
columns.  All NULL values are considered different from each other and from
all other values for the purpose of determining uniqueness, hence a UNIQUE
column may contain multiple entries with the value of NULL.
The COLLATE clause specifies what text 
[collating function] to use when comparing text entries for the column.  
The built-in [BINARY] collating function is used by default.
<p>
The DEFAULT constraint specifies a default value to use when doing an [INSERT].
The value may be NULL, a string constant or a number. Starting with
[version 3.1.0],
the default value may also be one of the special case-independant
keywords CURRENT_TIME, CURRENT_DATE or CURRENT_TIMESTAMP. If the value is
NULL, a string constant or number, it is literally inserted into the column
whenever an INSERT statement that does not specify a value for the column is
executed. If the value is CURRENT_TIME, CURRENT_DATE or CURRENT_TIMESTAMP, then
the current UTC date and/or time is inserted into the columns. For
CURRENT_TIME, the format is HH:MM:SS. For CURRENT_DATE, YYYY-MM-DD. The format
for CURRENT_TIMESTAMP is "YYYY-MM-DD HH:MM:SS".
</p>

<tcl>hd_fragment rowid {INTEGER PRIMARY KEY} ROWID</tcl>
<p>Specifying a PRIMARY KEY normally just creates a UNIQUE index
on the corresponding columns.  However, if primary key is on a single column
that has datatype INTEGER, then that column is used internally
as the actual key of the B-Tree for the table.  This means that the column
may only hold unique integer values.  (Except for this one case,
SQLite ignores the datatype specification of columns and allows
any kind of data to be put in a column regardless of its declared
datatype.)  If a table does not have an INTEGER PRIMARY KEY column,
then the B-Tree key will be a automatically generated integer.
The B-Tree key for a row can always be accessed using one of the
special names "<b>ROWID</b>", "<b>OID</b>", or "<b>_ROWID_</b>".
This is true regardless of whether or not there is an INTEGER
PRIMARY KEY.  An INTEGER PRIMARY KEY column can also include the
keyword [AUTOINCREMENT].  The [AUTOINCREMENT] keyword modified the way
that B-Tree keys are automatically generated.  Additional detail
on automatic B-Tree key generation is available
<a href="autoinc.html">separately</a>.</p>

<p>According to the SQL standard, PRIMARY KEY should imply NOT NULL.
Unfortunately, due to a long-standing coding oversight, this is not 
the case in SQLite.  SQLite allows NULL values
in a PRIMARY KEY column.  We could change SQLite to conform to the
standard (and we might do so in the future), but by the time the
oversight was discovered, SQLite was in such wide use that we feared
breaking legacy code if we fixed the problem.  So for now we have
chosen to continue allowing NULLs in PRIMARY KEY columns.
Developers should be aware, however, that we may change SQLite to
conform to the SQL standard in future and should design new programs
accordingly.</p>

<p>If the "TEMP" or "TEMPORARY" keyword occurs in between "CREATE"
and "TABLE" then the table that is created is only visible
within that same database connection
and is automatically deleted when
the database connection is closed.  Any indices created on a temporary table
are also temporary.  Temporary tables and indices are stored in a
separate file distinct from the main database file.</p>

<p> If a &lt;database-name&gt; is specified, then the table is created in 
the named database. It is an error to specify both a &lt;database-name&gt;
and the TEMP keyword, unless the &lt;database-name&gt; is "temp". If no
database name is specified, and the TEMP keyword is not present,
the table is created in the main database.</p>

<p>The optional [conflict clause] following each constraint
allows the specification of an alternative default
constraint conflict resolution algorithm for that constraint.
The default is abort ABORT.  Different constraints within the same
table may have different default conflict resolution algorithms.
If an [INSERT] or [UPDATE] statement specifies a different conflict
resolution algorithm, then that algorithm is used in place of the
default algorithm specified in the CREATE TABLE statement.
See the section titled
[ON CONFLICT] for additional information.</p>

<p>CHECK constraints are supported as of [version 3.3.0].  Prior
to version 3.3.0, CHECK constraints were parsed but not enforced.</p>

<p>The number of columns in a table is limited by the
[SQLITE_MAX_COLUMN] compile-time parameter.
A single row of a table cannot store more than
[SQLITE_MAX_LENGTH] bytes of data.
Both of these limits can be lowered at runtime using the
[sqlite3_limit()] C/C++ interface.</p>


<p>The CREATE TABLE AS form defines the table to be
the result set of a query.  The names of the table columns are
the names of the columns in the result.</p>

<p>The text
of each CREATE TABLE statement is stored in the <b>sqlite_master</b>
table.  Every time the database is opened, all CREATE TABLE statements
are read from the <b>sqlite_master</b> table and used to regenerate
SQLite's internal representation of the table layout.
If the original command was a CREATE TABLE AS then then an equivalent
CREATE TABLE statement is synthesized and store in <b>sqlite_master</b>
in place of the original command.
The text of CREATE TEMPORARY TABLE statements are stored in the
<b>sqlite_temp_master</b> table.
</p>

<p>If the optional IF NOT EXISTS clause is present and another table
with the same name aleady exists, then this command becomes a no-op.</p>

<p>Tables are removed using the <a href="lang_droptable.html">DROP TABLE</a> 
statement.  </p>

<tcl>
##############################################################################
Section {CREATE TRIGGER} createtrigger {{CREATE TRIGGER}}

BubbleDiagram create-trigger-stmt 1
</tcl>

<p>The CREATE TRIGGER statement is used to add triggers to the 
database schema. Triggers are database operations (the <i>trigger-action</i>) 
that are automatically performed when a specified database event (the
<i>database-event</i>) occurs.  </p>

<p>A trigger may be specified to fire whenever a [DELETE], [INSERT],
or [UPDATE] of a
particular database table occurs, or whenever an [UPDATE] of one or more
specified columns of a table are updated.</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 as <i>trigger-steps</i> 
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 <i>trigger-steps</i> 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
<i>trigger-event</i>s 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 as 
<i>trigger-steps</i> are only executed for rows for which the WHEN
clause is true. If no WHEN clause is supplied, the SQL statements
are executed for all rows.</p>

<p>The specified <i>trigger-time</i> determines when the <i>trigger-steps</i>
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]
<i>trigger-step</i>. However if an [ON CONFLICT] clause is specified as part of 
the statement causing the trigger to fire, then this conflict handling
policy is used instead.</p>

<p>Triggers are automatically dropped when the table that they are 
associated with is dropped.</p>

<tcl>hd_fragment instead_of_trigger {INSTEAD OF} {INSTEAD OF trigger}</tcl>
<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. Thereafter,
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><b>Example:</b></p>

<p>Assuming that customer records are stored in the "customers" table, and
that order records are stored in the "orders" table, the following 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>Note that currently, triggers may behave oddly when created on tables
  with [INTEGER PRIMARY KEY] fields. If a BEFORE trigger program modifies the 
  [INTEGER PRIMARY KEY] field of a row that will be subsequently updated by the
  statement that causes the trigger to fire, then the update may not occur. 
  The workaround is to declare the table with a PRIMARY KEY column instead
  of an [INTEGER PRIMARY KEY] column.</p>

<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 the first three forms is called during trigger-program
execution, the specified [ON CONFLICT] processing is performed
(either ABORT, FAIL or ROLLBACK) and 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 of 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>

<p>Triggers are removed using the [DROP TRIGGER] statement.</p>


<tcl>
###############################################################################
Section {CREATE VIEW} {createview} {{CREATE VIEW} view views}

BubbleDiagram create-view-stmt 1
</tcl>

<p>The CREATE VIEW command assigns a name to a pre-packaged 
<a href="lang_select.html">SELECT</a>
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
process that opened the database and is automatically deleted when
the database is closed.</p>

<p> If a &lt;database-name&gt; is specified, then the view is created in 
the named database. It is an error to specify both a &lt;database-name&gt;
and the TEMP keyword, unless the &lt;database-name&gt; is "temp". If no
database name is specified, and the TEMP keyword is not present,
the table 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>

<tcl>
##############################################################################
Section {CREATE VIRTUAL TABLE} {createvtab} {{CREATE VIRTUAL_TABLE}}

BubbleDiagram create-virtual-table-stmt 1
</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.
Virtual tables cannot be used in
[sqlite3_enable_shared_cache | shared cache mode].</p>

<p>The &lt;module-name&gt; is the name of an object that implements
the virtual table.  The &lt;module-name&gt; must be registered with
the SQLite database connection using
sqlite3_create_module()
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 module 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>

<tcl>
##############################################################################
Section DELETE delete {DELETE DELETEs}

BubbleDiagram delete-stmt 1
</tcl>

<p>The DELETE command is used to remove records from a table.
The command consists of the "DELETE FROM" keywords followed by
the name of the table from which records are to be removed.
</p>

<p>Without a WHERE clause, all rows of the table are removed.
If a WHERE clause is supplied, then only those rows that match
the expression are removed.</p>

<p>When the WHERE clause is omitted from a DELETE statement,
SQLite uses an optimization to erase the entire table content
without having to visit each row of the table individual.
This "truncate" optimization makes the delete run much faster.
However, it also means that the [sqlite3_changes()] interface
and the [count_changes] PRAGMA
will not actually return the number of deleted rows.  If you
need to delete every row of a table and still have
[sqlite3_changes()] and [count_changes] work correctly, then
use WHERE clause that is always true:</p>

<blockquote><pre>
DELETE FROM sometable WHERE 1;
</pre></blockquote>

<p>The optional LIMIT clause can be used to limit the number of
rows deleted, and thereby limit the size of the transaction.
The ORDER BY clause is used only to determine which rows fall
within the LIMIT.  The order in which rows are deleted is arbitrary
and is not determined by the ORDER BY clause.</p>

<tcl>
###############################################################################
Section {DETACH DATABASE} detach DETACH

BubbleDiagram detach-stmt 1
</tcl>

<p>This statement detaches an additional database connection previously 
attached using the [ATTACH] statement.  
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>This statement will fail if SQLite is in the middle of a transaction.</p>


<tcl>
##############################################################################
Section {DROP INDEX} dropindex {{DROP INDEX}}

BubbleDiagram drop-index-stmt 1
</tcl>

<p>The DROP INDEX statement removes an index added
with the [CREATE INDEX] statement.  The index named is completely removed from
the disk.  The only way to recover the index is to reenter the
appropriate [CREATE INDEX] command.</p>

<p>The DROP INDEX statement does not reduce the size of the database 
file in the default mode.
Empty space in the database is retained for later [INSERT] statements.  To 
remove free space in the database, use the [VACUUM]
command.  If [auto_vacuum] mode is enabled for a database then space
will be freed automatically by DROP INDEX.</p>


<tcl>
##############################################################################
Section {DROP TABLE} droptable {{DROP TABLE}}

BubbleDiagram drop-table-stmt 1
</tcl>

<p>The DROP TABLE statement removes a table added with the
[CREATE TABLE] statement.  The name specified is the
table name.  It 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 DROP TABLE statement does not reduce the size of the database 
file in the default mode.  Empty space in the database is retained for
later [INSERT] statements.  To 
remove free space in the database, 
use the [VACUUM] statement.
If [auto_vacuum] mode is enabled for a database then space
will be freed automatically by DROP TABLE.</p>

<p>The optional IF EXISTS clause suppresses the error that would normally
result if the table does not exist.</p>

<tcl>
##############################################################################
Section {DROP TRIGGER} droptrigger {{DROP TRIGGER}}

BubbleDiagram drop-trigger-stmt 1
</tcl>

<p>The DROP TRIGGER statement removes a trigger created by the 
[CREATE TRIGGER] statement.  The trigger is 
deleted from the database schema. Note that triggers are automatically 
dropped when the associated table is dropped.</p>

<tcl>
##############################################################################
Section {DROP VIEW} dropview {{DROP VIEW}}

BubbleDiagram drop-view-stmt 1
</tcl>

<p>The DROP VIEW statement removes a view created by the
[CREATE VIEW] statement.  The name specified is the 
view name.  It is removed from the database schema, but no actual data 
in the underlying base tables is modified.</p>

<tcl>
##############################################################################
Section EXPLAIN explain EXPLAIN

BubbleDiagram sql-stmt
</tcl>

<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>When the EXPLAIN keyword appears by itself it causes the statement
to behave as a query that returns the sequence of 
<a href="opcode.html">virtual machine instructions</a> 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 about what indices would have been used.</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 behavior is undocumented, unspecified, and variable.</p>

<tcl>
##############################################################################
Section expression expr {expression {expression syntax}}

BubbleDiagram expr 1
BubbleDiagram literal-value
BubbleDiagram signed-number
BubbleDiagram raise-function
</tcl>

<p>This section is different from the others.  Most other sections of
this document talks about a particular SQL command.  This section does
not talk about a standalone command but about "expressions" which are 
subcomponents of most other commands.</p>

<p>SQLite understands the following binary operators, in order from
highest to lowest precedence:</p>

<blockquote><pre>
<font color="#2c2cf0"><big>||
*    /    %
+    -
&lt;&lt;   &gt;&gt;   &amp;    |
&lt;    &lt;=   &gt;    &gt;=
=    ==   !=   &lt;&gt;   </big>IN
AND   
OR</font>
</pre></blockquote>

<p>Supported unary prefix operators are these:</p>

<blockquote><pre>
<font color="#2c2cf0"><big>-    +    ~    NOT</big></font>
</pre></blockquote>

<p>The COLLATE operator can be thought of as a unary postfix
operator.  The COLLATE operator has the highest precedence.
It always binds more tightly than any prefix unary operator or
any binary operator.</p>

<tcl>hd_puts "
<p>The unary operator [Operator +] is a no-op.  It can be applied
to strings, numbers, or blobs and it always gives as its result the
value of 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 {&lt;&gt;}].
The [Operator ||] operator is \"concatenate\" - it joins together
the two strings of its operands.
The operator [Operator %] outputs the remainder of its left 
operand modulo its right operand.</p>

<p>The result of any binary operator is a numeric value, except
for the [Operator ||] concatenation operator which gives a string
result.</p>"</tcl>

<a name="literal_value"></a>
<p>
A literal value is an integer number or a floating point number.
Scientific notation is supported.  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.  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.
BLOB literals are string literals containing hexadecimal data and
preceded by a single "x" or "X" character.  For example:</p>

<blockquote><pre>
X'53514C697465'
</pre></blockquote>

<p>
A literal value can also be the token "NULL".
</p>

<p>
A parameter specifies a placeholder in the expression for a literal
value that is filled in at runtime using the
[sqlite3_bind_blob() | sqlite3_bind()] APIs.
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 holds a spot for
the next unused parameter.</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 named
parameter with the name AAAA.  Named parameters are also numbered.
The number assigned is the next unused number.  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.</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 occurances of "::" and a suffix enclosed in "(...)" containing
any text at all.  This syntax is the form of a variable name in the Tcl
programming language.</td>
</tr>
</table>
</blockquote>

<p>Parameters that are not assigned values using
[sqlite3_bind_blob() | sqlite3_bind()] are treated
as NULL.</p>

<tcl>hd_fragment like LIKE ESCAPE</tcl>
<p>The LIKE operator does a pattern matching comparison. The operand
to the right contains the pattern, the left hand operand contains the
string to match against the pattern. 

<tcl>hd_puts "A percent symbol [Operator %] in the pattern matches any
sequence of zero or more characters in the string.  An underscore
[Operator _] in the pattern matches any single character in the
string.  Any other character matches itself or it's lower/upper case
equivalent (i.e. case-insensitive matching).  (A bug: SQLite only
understands upper/lower case for 7-bit Latin characters.  Hence the
LIKE operator is case sensitive for 8-bit iso8859 characters or UTF-8
characters.  For example, the expression <b>'a'&nbsp;LIKE&nbsp;'A'</b>
is TRUE but <b>'&aelig;'&nbsp;LIKE&nbsp;'&AElig;'</b> is FALSE.).</p>"</tcl>

<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 itself matches a
literal percent symbol, underscore or escape character in the string,
respectively. 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>

The LIKE operator is not case sensitive and will match upper case
characters on one side against lower case characters on the other.  
(A bug: SQLite only understands upper/lower case for 7-bit Latin
characters.  Hence the LIKE operator is case sensitive for 8-bit
iso8859 characters or UTF-8 characters.  For example, the expression
<b>'a'&nbsp;LIKE&nbsp;'A'</b> is TRUE but
<b>'&aelig;'&nbsp;LIKE&nbsp;'&AElig;'</b> is FALSE.).</p>

<p>The infix LIKE
operator is implemented by calling the user function <a href="#likeFunc">
like(<i>X</i>,<i>Y</i>)</a>.  If an ESCAPE clause is present, it adds
a third parameter to the function call. If the functionality of LIKE can be
overridden by defining an alternative implementation of the
like() SQL function.</p>
</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 a user-defined function named "regexp"
is added at run-time, that function will be called in order
to implement the REGEXP operator.</p>

<tcl>hd_fragment match MATCH</tcl>
<p>The MATCH operator is a special syntax for the match()
user function.  The default match() function implementation
raises and exception and is not really useful for anything.
But extensions can override the match() function with more
helpful logic.</p>

<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>".
These special identifiers all describe the
unique integer key (the "row key") associated with every 
row of every table.
The special identifiers only refer to the row key if the [CREATE TABLE]
statement does not define a real column with the same name.  Row keys
act like read-only columns.  A row key can be used anywhere a regular
column can be used, except that you cannot change the value
of a row key in an [UPDATE] or [INSERT] statement.
"SELECT * ..." does not return the row key.</p>

<p>[SELECT] statements can appear in expressions as either the
right-hand operand of the IN operator, as a scalar quantity, or
as the operand of an EXISTS operator.
As a scalar quantity or the operand of an IN operator,
the SELECT should have only a single column in its
result.  Compound SELECTs (connected with keywords like UNION or
EXCEPT) are allowed.
With the EXISTS operator, the columns in the result set of the [SELECT] are
ignored and the expression returns TRUE if one or more rows exist
and FALSE if the result set is empty.
If no terms in the [SELECT] expression refer to value in the containing
query, then the expression is evaluated once prior to any other
processing and the result is reused as necessary.  If the [SELECT] expression
does contain variables from the outer query, then the [SELECT] is reevaluated
every time it is needed.</p>

<p>When a SELECT is the right operand of the IN operator, the IN
operator returns TRUE if the result of the left operand is any of
the values generated by the select.  The IN operator may be preceded
by the NOT keyword to invert the sense of the test.</p>

<p>When a SELECT appears within an expression but is not the right
operand of an IN operator, then the first row of the result of the
SELECT becomes the value used in the expression.  If the SELECT yields
more than one result row, all rows after the first are ignored.  If
the SELECT yields no rows, then the value of the SELECT is NULL.</p>

<p>A CAST expression changes the datatype of the <expr> into the
type specified by &lt;type&gt;. 
&lt;type&gt; can be any non-empty type name that is valid
for the type in a column definition of a [CREATE TABLE] statement.</p>

<p>Both [corefunc|simple] and [aggfunc|aggregate] functions are supported.
(For presentation purposes, simple functions are further subdivided into
[corefunc | core functions] and [datefunc | date-time functions].)
A simple function can be used in any expression.  Simple functions return
a result immediately based on their inputs.  Aggregate functions
may only be used in a SELECT statement.  Aggregate functions compute
their result across all rows of the result set.</p>

<tcl>
##############################################################################
Section {Core Functions} corefunc {corefunc}
proc funcdef {syntax keywords desc} {
  hd_puts {<tr>}
  regsub -all {\s+} [string trim $syntax] {<br></br>} syntax
  regsub -all {\(([^*)]+)\)} $syntax {(<i>\1</i>)} syntax
  regsub -all {,} $syntax {</i>,<i>} syntax
  regsub -all {<i>\.\.\.</i>} $syntax {...} syntax
  hd_puts "<td valign=\"top\" align=\"right\" width=\"120\">$syntax</td>"
  hd_puts {<td valign="top">}
  if {[llength $keywords]==0} {
    regexp {[a-z_]+} $syntax name
    hd_fragment $name $name
  } else {
    eval hd_fragment $keywords
    hd_keywords $keywords
  }
  hd_resolve $desc
  hd_puts {</td></tr>}
}
</tcl>

<p>The core functions shown below are available by default. 
[datefunc | Date &amp; Time functions] and
[aggfunc | aggregate 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>

<table border=0 cellpadding=10>
<tcl>
funcdef {abs(X)} {} {
  Return the absolute value of the numeric
  argument <i>X</i>.  Return NULL if <i>X</i> is NULL.  Return 0.0 if
  <i>X</i> is not a numeric value.
}

funcdef {coalesce(X,Y,...)} {} {
  Return a copy of the first non-NULL argument.  If
  all arguments are NULL then NULL is returned.  There must be at least 
  2 arguments.
}

funcdef {glob(X,Y)} {} {
  This function is used to implement the
  "<b>Y GLOB X</b>" syntax of SQLite.
  Note that the X and Y arguments are reversed in the glob() function
  relative to the infix [GLOB] operator.
  The [sqlite3_create_function()]
  interface can
  be used to override this function and thereby change the operation
  of the [GLOB] operator.</td>
}

funcdef {ifnull(X,Y)} {} {
  Return a copy of the first non-NULL argument.  If
  both arguments are NULL then NULL is returned. This behaves the same as 
  [coalesce()].</td>
}

funcdef {hex(X)} {} {
  The argument is interpreted as a BLOB.  The result
  is a hexadecimal rendering of the content of that blob.
}

funcdef {last_insert_rowid()} {} {
  Return the [ROWID]
  of the last row insert from this
  connection to the database. 
  This is the same value that would be returned
  from the [sqlite3_last_insert_rowid()] API function.
}

funcdef {length(X)} {} {
  Return the string length of <i>X</i> in characters.
  If SQLite is configured to support UTF-8, then the number of UTF-8
  characters is returned, not the number of bytes.
}

funcdef {like(X,Y) like(X,Y,Z)} {} {
  This function is used to implement the "<b>Y LIKE X &#91;ESCAPE Z&#93;</b>"
  syntax of SQL. If the optional ESCAPE clause is present, then the
  user-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.
  The [sqlite3_create_function()] interface can be used to override this
  function and thereby change the operation of the
  [LIKE] operator. When doing this, 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 {load_extension(X) load_extension(X,Y)} {load_extension} {
  Load SQLite extensions out of the shared library
  file named <i>X</i> using the entry point <i>Y</i>.  The result
  is a NULL.  If <i>Y</i> is omitted then the default entry point
  of <b>sqlite3_extension_init</b> is used.  This function raises
  an exception if the extension fails to load or initialize correctly.

  <p>This function will fail if the extension attempts to modify
  or delete a 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>
}

funcdef {lower(X)} {} {
  Return a copy of string <i>X</i> with all ASCII characters
  converted to lower case.  The C library <b>tolower()</b> routine is used
  for the conversion, which means that this function might not
  work correctly on non-ASCII UTF-8 characters.
}

funcdef {ltrim(X) ltrim(X,Y)} {} {
  Return a string formed by removing any and all
  characters that appear in <i>Y</i> from the left side of <i>X</i>.
  If the <i>Y</i> argument is omitted, spaces are removed.
}

funcdef {max(X,Y,...)} {maxCoreFunc max} {
  Return the argument with the maximum value.  Arguments
  may be strings in addition to numbers.  The maximum value is determined
  by the usual sort order.  Note that <b>max()</b> is a simple function when
  it has 2 or more arguments but converts to an aggregate function if given
  only a single argument.
}

funcdef {min(X,Y,...)} {minCoreFunc min} {
  Return the argument with the minimum value.  Arguments
  may be strings in addition to numbers.  The minimum value is determined
  by the usual sort order.  Note that <b>min()</b> is a simple function when
  it has 2 or more arguments but converts to an aggregate function if given
  only a single argument.
}

funcdef {nullif(X,Y)} {} {
  Return the first argument if the arguments are different, 
  otherwise return NULL.
}

funcdef {quote(X)} {} {
  This routine returns a string which is the value of
  its argument suitable for inclusion into another SQL statement.
  Strings are surrounded by single-quotes with escapes on interior quotes
  as needed.  BLOBs are encoded as hexadecimal literals.
  The implementation of [VACUUM] uses this function. The function
  is also useful when writing triggers to implement undo/redo functionality.
}

funcdef {random()} {} {
  Return a pseudo-random integer
  between -9223372036854775808 and +9223372036854775807.
}

funcdef {randomblob(N)} {} {
  Return an <i>N</i>-byte blob containing pseudo-random bytes.
  <i>N</i> should be a postive integer.

  <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)} {} {
  Return a string formed by substituting string <i>Z</i> for
  every occurrance of string <i>Y</i> in string <i>X</i>.  The [BINARY]
  collating sequence is used for comparisons.
}

funcdef {round(X) round(X,Y)} {} {
  Round off the number <i>X</i> to <i>Y</i> digits to the
  right of the decimal point.  If the <i>Y</i> argument is omitted, 0 is 
  assumed.
}

funcdef {rtrim(X) rtrim(X,Y)} {} {
  Return a string formed by removing any and all
  characters that appear in <i>Y</i> from the right side of <i>X</i>.
  If the <i>Y</i> argument is omitted, spaces are removed.
}

funcdef {soundex(X)} {} {
  Compute the soundex encoding of the string <i>X</i>.
  The string "?000" is returned if the argument is NULL.
  This function is omitted from SQLite by default.
  It is only available the -DSQLITE_SOUNDEX=1 compiler option
  is used when SQLite is built.
}

funcdef {sqlite_version(X)} {sqlite_version} {
  Return the version string for the SQLite library
  that is running.  Example:  "3.5.9"
}

funcdef {substr(X,Y,Z) substr(X,Y)} {} {
  Return a substring of input string <i>X</i> that begins
  with the <i>Y</i>-th character and which is <i>Z</i> characters long.
  If <i>Z</i> is omitted then all character through the end of the string
  are returned.
  The left-most character of <i>X</i> is number 1.  If <i>Y</i> is negative
  the the first character of the substring is found by counting from the
  right rather than the left.  If <i>X</i> is string
  then characters indices refer to actual UTF-8 characters.  If
  <i>X</i> is a BLOB then the indices refer to bytes.
}

funcdef {trim(X) trim(X,Y)} {} {
  Return a string formed by removing any and all
  characters that appear in <i>Y</i> from both ends of <i>X</i>.
  If the <i>Y</i> argument is omitted, spaces are removed.
}

funcdef {typeof(X)} {} {
  Return the type of the expression <i>X</i>.  The only 
  return values are "null", "integer", "real", "text", and "blob".
  SQLite's type handling is 
  explained in <a href="datatype3.html">Datatypes in SQLite Version 3</a>.
}

funcdef {upper(X)} {} {
  Return a copy of input string <i>X</i> converted to all
  upper-case letters.  The implementation of this function uses the C library
  routine <b>toupper()</b> which means it may not work correctly on 
  non-ASCII UTF-8 strings.
}

funcdef {zeroblob(N)} {} {
  Return 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].
}
</tcl>
</table>

<tcl>
##############################################################################
Section {Date And Time Functions} datefunc {datefunc}
</tcl>

<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 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() 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 
<a href="http://en.wikipedia.org/wiki/Julian_day">julian day</a> - 
number of days since noon in Greenwich on November 24, 4714 B.C. 
(<a href="http://en.wikipedia.org/wiki/Proleptic_Gregorian_calendar">
Proleptic Gregorian calendar</a>). 
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 
<a href="http://opengroup.org/onlinepubs/007908799/xsh/strftime.html">
strftime() function</a> 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>

<h3>Time Strings</h3>

<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 
<a href="http://www.w3c.org/TR/NOTE-datetime">ISO-8601</a>. 
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.
<a href="http://en.wikipedia.org/wiki/Coordinated_Universal_Time">
Universal Coordinated Time (UTC)</a> is used. 
Format 12 is the 
<a href="http://en.wikipedia.org/wiki/Julian_day">julian day number</a>
expressed as a floating point value.
</p>

<h3>Modifiers</h3>

<p>The time string can be followed by zero or more modifiers that 
alter the date or alter the interpretation of the date. 
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 
specified by the preceding timestring.</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 to the next date 
where the weekday number is N. Sunday is 0, Monday is 1, and so forth.</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
<a href="http://en.wikipedia.org/wiki/Unix_time">Unix Time</a> - the 
number of seconds since 1970.</p>

<p>The "localtime" modifier (12) adjusts the previous time
string so that it displays the correct local time. "utc" undoes this.</p>

<h3>Examples</h3>

<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 Independent.</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>

<h3>Caveats And Bugs</h3>

<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>Date computations do not give correct results for dates 
before Julian day number 0 (-4713-11-24 12:00:00).</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 
<a href="http://en.wikipedia.org/wiki/Gregorian_calendar">
Gregorian calendar</a> system.  It is also assumed that every
day is exactly 86400 seconds in duration.</p>

<tcl>
##############################################################################
Section {Aggregate Functions} aggfunc {aggfunc}
</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 preceeded 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>

<table border=0 cellpadding=10>
<tcl>
funcdef {avg(X)} {} {
  Return 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 even if all
  inputs are integers.
}

funcdef {count(X) count(*)} {} {
  The first form return a count of the number of times
  that <i>X</i> is not NULL in a group.  The second form (with no argument)
  returns the total number of rows in the group.
}

funcdef {group_concat(X) group_concat(X,Y)} {} {
  The result is a string which is the concatenation of
  all non-NULL values of <i>X</i>.  If parameter <i>Y</i> is the separator
  between instances of <i>X</i>.  A comma (",") is used as the separator
  if <i>Y</i> is omitted.
}

funcdef {max(X)} {maxAggFunc agg_max} {
  Return the maximum value of all values in the group.
  The usual sort order is used to determine the maximum.
}

funcdef {min(X)} {minAggFunc agg_min} {
  Return the minimum non-NULL value of all values in the group.
  The usual sort order is used to determine the minimum.  
  NULL is only returned
  if all values in the group are NULL.
}

funcdef {sum(X) total(X)} {sumFunc sum total} {
  Return the numeric 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 exception.
}
</tcl>
</table>

<tcl>
##############################################################################
Section INSERT insert {INSERT INSERTs}

BubbleDiagram insert-stmt 1
</tcl>

<p>The INSERT statement comes in two basic forms.  The first form
(with the "VALUES" keyword) creates a single new row in an existing table.
If no column-list is specified then the number of values must
be the same as the number of columns in the table.  If a column-list
is specified, then the number of values must match the number of
specified columns.  Columns of the table that do not appear in the
column list are filled with the default value, or with NULL if no
default value is specified.
</p>

<p>The second form of the INSERT statement takes it data from a
SELECT statement.  The number of columns in the result of the
SELECT must exactly match the number of columns in the table if
no column list is specified, or it must match the number of columns
name in the column list.  A new entry is made in the table
for every row of the SELECT result.  The SELECT may be simple
or compound.</p>

<p>The optional conflict-clause allows the specification of an alternative
constraint conflict resolution algorithm to use during this one command.
See the section titled
[ON CONFLICT] for additional information.
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>

<tcl>
##############################################################################
Section {ON CONFLICT clause} conflict {{conflict clause} {ON CONFLICT}}

BubbleDiagram conflict-clause
</tcl>

<p>The ON CONFLICT clause is not a separate SQL command.  It is a
non-standard clause 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 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", to make
the syntax seem more natural.  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 specifies an algorithm used to resolve
constraint conflicts.  There are five choices: ROLLBACK, ABORT,
FAIL, IGNORE, and REPLACE. The default algorithm is ABORT.  This
is what they mean:</p>

<dl>
<dt><b>ROLLBACK</b></dt>
<dd><p>When a constraint violation occurs, an immediate ROLLBACK
occurs, thus ending the current transaction, and the command aborts
with a return code of SQLITE_CONSTRAINT.  If no transaction is
active (other than the implied transaction that is created on every
command) then this algorithm works the same as ABORT.</p></dd>

<dt><b>ABORT</b></dt>
<dd><p>When a constraint violation occurs, the command backs out
any prior changes it might have made and aborts with a return code
of SQLITE_CONSTRAINT.  But no ROLLBACK is executed so changes
from prior commands within the same transaction
are preserved.  This is the default behavior.</p></dd>

<dt><b>FAIL</b></dt>
<dd><p>When a constraint violation occurs, the command aborts with a
return code SQLITE_CONSTRAINT.  But any changes to the database that
the command made prior to encountering the constraint violation
are preserved and are not backed out.  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></dd>

<dt><b>IGNORE</b></dt>
<dd><p>When a constraint violation occurs, the one row that contains
the constraint violation is not inserted or changed.  But the command
continues executing normally.  Other rows before and after the row that
contained the constraint violation continue to be inserted or updated
normally.  No error is returned.</p></dd>

<dt><b>REPLACE</b></dt>
<dd><p>When a UNIQUE constraint violation occurs, the pre-existing rows
that are causing the constraint violation are removed prior to inserting
or updating the current row.  Thus the insert or update always occurs.
The command continues executing normally.  No error is returned.
If a NOT NULL constraint violation occurs, the NULL value is replaced
by the default value for that column.  If the column has no default
value, then the ABORT algorithm is used.  If a CHECK constraint violation
occurs then the IGNORE algorithm is used.</p>

<p>When this conflict resolution strategy deletes rows in order to
satisfy a constraint, it does not invoke delete triggers on those
rows.  This behavior might change in a future release.</p>
</dl>

<p>The algorithm specified in the OR clause of a INSERT or UPDATE
overrides any algorithm specified in a CREATE TABLE.
If no algorithm is specified anywhere, the ABORT algorithm is used.</p>

<tcl>
##############################################################################
Section REINDEX reindex REINDEX

BubbleDiagram reindex-stmt 1
</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>In the first form, all indices in all attached databases that use the
named collation sequence are recreated. In the second form, if 
<i>&#91;database-name.&#93;table/index-name</i> identifies a table,
then all indices
associated with the table are rebuilt. If an index is identified, then only
this specific index is deleted and recreated.
</p>

<p>If no <i>database-name</i> is specified and there exists both a table or
index and a collation sequence of the specified name, then indices associated
with the collation sequence only are reconstructed. This ambiguity may be
dispelled by always specifying a <i>database-name</i> when reindexing a
specific table or index.

<tcl>
###############################################################################
Section REPLACE replace REPLACE

</tcl>

<p>The REPLACE command is an alias for the "INSERT OR REPLACE" variant
of the <a href="lang_insert.html">INSERT</a> command.  
This alias is provided for
compatibility with MySQL.  See the 
<a href="lang_insert.html">INSERT</a> command documentation for additional
information.</p>  

<tcl>
###############################################################################
Section SELECT select {SELECT query}

BubbleDiagram select-stmt 1
BubbleDiagram result-column
BubbleDiagram join-source
BubbleDiagram single-source
BubbleDiagram join-op
BubbleDiagram join-constraint
BubbleDiagram ordering-term
BubbleDiagram compound-operator
</tcl>

<p>The SELECT statement is used to query the database.  The
result of a SELECT is zero or more rows of data where each row
has a fixed number of columns.  The number of columns in the
result is specified by the expression list in between the
SELECT and FROM keywords.  Any arbitrary expression can be used
as a result.  If a result expression is }
hd_puts "[Operator *] then all columns of all tables are substituted\n"
hd_puts "for that one expression.  If the expression is the name of\n"
hd_puts "a table followed by [Operator .*] then the result is all columns\n"
hd_puts {in that one table.</p>

<p>The DISTINCT keyword causes a subset of result rows to be returned, 
in which each result row is different.  NULL values are not treated as 
distinct from each other.  The default behavior is that all result rows 
be returned, which can be made explicit with the keyword ALL.</p>

<p>The query is executed against one or more tables specified after
the FROM keyword.  If multiple tables names are separated by commas,
then the query is against the cross join of the various tables.
The full SQL-92 join syntax can also be used to specify joins.
A sub-query
in parentheses may be substituted for any table name in the FROM clause.
The entire FROM clause may be omitted, in which case the result is a
single row consisting of the values of the expression list.
</p>

<p>The WHERE clause can be used to limit the number of rows over
which the query operates.</p>

<p>The GROUP BY clause causes one or more rows of the result to
be combined into a single row of output.  This is especially useful
when the result contains aggregate functions.  The expressions in
the GROUP BY clause do <em>not</em> have to be expressions that
appear in the result.  The HAVING clause is similar to WHERE except
that HAVING applies after grouping has occurred.  The HAVING expression
may refer to values, even aggregate functions, that are not in the result.</p>

<p>The ORDER BY clause causes the output rows to be sorted.  
The argument to ORDER BY is a list of expressions that are used as the
key for the sort.  The expressions do not have to be part of the
result for a simple SELECT, but in a compound SELECT each sort
expression must exactly match one of the result columns.  Each
sort expression may be optionally followed by a COLLATE keyword and
the name of a collating function used for ordering text and/or
keywords ASC or DESC to specify the sort order.</p>

<p>Each term of an ORDER BY expression is processed as follows:</p>

<ol>
<li><p>If the ORDER BY expression is a constant integer K then the
output is ordered by the K-th column of the result set.</p></li>
<li><p>If the ORDER BY expression is an identifier and one of the
output columns as an alias by the same name, then the output is
ordered by the identified column.</p></li>
<li><p>Otherwise, the ORDER BY expression is evaluated and the output 
is ordered by the value of that expression.</p></li>
</ol>

<p>In a compound SELECT statement, the third ORDER BY matching rule
requires that the expression be identical to one of the columns in
the result set.  The three rules are first applied to the left-most
SELECT in the compound.  If a match is found, the search stops.  Otherwise,
the next SELECT to the right is tried.  This continues until a match
is found.  Each term of the ORDER BY clause is processed separately 
and may come from different SELECT statements in the compound.</p>

<p>The LIMIT clause places an upper bound on the number of rows
returned in the result.  A negative LIMIT indicates no upper bound.
The optional OFFSET following LIMIT specifies how many
rows to skip at the beginning of the result set.
In a compound query, the LIMIT clause may only appear on the
final SELECT statement.
The limit is applied to the entire query not
to the individual SELECT statement to which it is attached.
Note that if the OFFSET keyword is used in the LIMIT clause, then the
limit is the first number and the offset is the second number.  If a
comma is used instead of the OFFSET keyword, then the offset is the
first number and the limit is the second number.  This seeming
contradition is intentional - it maximizes compatibility with legacy
SQL database systems.
</p>

<p>A compound SELECT is formed from two or more simple SELECTs connected
by one of the operators UNION, UNION ALL, INTERSECT, or EXCEPT.  In
a compound SELECT, all the constituent SELECTs must specify the
same number of result columns.  There may be only a single ORDER BY
clause at the end of the compound SELECT.  The UNION and UNION ALL
operators combine the results of the SELECTs to the right and left into
a single big table.  The difference is that in UNION all result rows
are distinct where in UNION ALL there may be duplicates.
The INTERSECT operator takes the intersection of the results of the
left and right SELECTs.  EXCEPT takes the result of left SELECT after
removing the results of the right SELECT.  When three or more SELECTs
are connected into a compound, they group from left to right.</p>


<tcl>
##############################################################################
Section UPDATE update {UPDATE UPDATEs}

BubbleDiagram update-stmt 1
</tcl>

<p>The UPDATE statement is used to change the value of columns in 
selected rows of a table.  Each assignment in an UPDATE specifies
a column name to the left of the equals sign and an arbitrary expression
to the right.  The expressions may use the values of other columns.
All expressions are evaluated before any assignments are made.
A WHERE clause can be used to restrict which rows are updated.</p>

<p>The optional conflict-clause allows the specification of an alternative
constraint conflict resolution algorithm to use during this one command.
See the section titled
[ON CONFLICT] for additional information.</p>

<p>The optional LIMIT clause can be used to limit the number of
rows modifed, and thereby limit the size of the transaction.
The ORDER BY clause is used only to determine which rows fall
within the LIMIT.  The order in which rows are modified is arbitrary
and is not determined by the ORDER BY clause.</p>

<tcl>
##############################################################################
Section VACUUM vacuum VACUUM

BubbleDiagram vacuum-stmt 1
</tcl>

<p>When an object (table, index, or trigger) is dropped from the 
database, it leaves behind empty space.  This makes the database 
file larger than it needs to be, but can speed up inserts.  In time 
inserts and deletes can leave the database file structure fragmented, 
which slows down disk access to the database contents.</p>

<p>The VACUUM command cleans
the main database by copying its contents to a temporary database file and 
reloading the original database file from the copy.  This eliminates 
free pages,  aligns table data to be contiguous, and otherwise cleans 
up the database file structure.</p>

<p>The VACUUM command may change the 
<a href="lang_createtable.html#rowid">ROWID</a> of entires in tables that do
not have an explicit INTEGER PRIMARY KEY.</p>

<p>VACUUM only works on the main database.
It is not possible to VACUUM an attached database file.</p>

<p>The VACUUM command will fail if there is an active transaction.
The VACUUM command is a no-op for in-memory databases.</p>

<p>As of SQLite version 3.1, an alternative to using the VACUUM command
is auto-vacuum mode, enabled using the 
[auto_vacuum] pragma.  When [auto_vacuum] is enabled for a database, 
large deletes cause
the size of the database file to shrink.  However, [auto_vacuum]
also causes excess fragmentation of the database file.  And [auto_vacuum]
does not compact partially filled pages of the database as VACUUM
does.
</p>

<tcl>
#############################################################################
# A list of keywords.  A asterisk occurs after the keyword if it is on
# the fallback list.
#
set keyword_list [lsort {
   ABORT*
   ADD
   AFTER*
   ALL
   ALTER
   ANALYZE*
   AND
   AS
   ASC*
   ATTACH*
   AUTOINCREMENT
   BEFORE*
   BEGIN*
   BETWEEN
   BY
   CASCADE*
   CASE
   CAST*
   CHECK
   COLLATE
   COLUMN
   COMMIT
   CONFLICT*
   CONSTRAINT
   CREATE
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   FOREIGN
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   GROUP
   HAVING
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   IGNORE*
   IMMEDIATE*
   IN
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   INDEXED*
   INITIALLY*
   INNER
   INSERT
   INSTEAD*
   INTERSECT
   INTO
   IS
   ISNULL
   JOIN
   KEY*
   LEFT
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   LIMIT
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   NATURAL
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   ON
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   PRIMARY
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   REFERENCES
   REGEXP
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   RIGHT
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}]

hd_puts {<DIV class="pdf_section">}
Section {SQLite Keywords} keywords {{SQL keyword} {SQL keywords}}
hd_puts {</DIV>}
</tcl>

<p>The SQL standard specifies a huge 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 three 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 interpreted as a literal string
        if it occurs in a context where a string literal is allowed, otherwise
	it is understood as an identifier.</td></tr>
<tr>	<td valign="top"><b>"keyword"</b></td><td></td>
	<td>A keyword in double-quotes is interpreted as an identifier if
        it matches a known identifier.  Otherwise it is interpreted as a
        string literal.</td></tr>
<tr>	<td valign="top"><b>&#91;keyword&#93;</b></td><td></td>
	<td>A keyword enclosed in square brackets is always understood as
        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>
</table>
</blockquote>
</p>

<p>Quoted keywords are unaesthetic.
To help you avoid them, SQLite allows many keywords to be used unquoted
as the names of databases, tables, indices, triggers, views, columns,
user-defined functions, collations, attached databases, and virtual
function modules.
In the list of keywords that follows, those that can be used as identifiers
are shown in an italic font.  Keywords that must be quoted in order to be
used as identifiers are shown in bold.</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 indentifier that is an English language word, even if
you do not have to.
</p>

<p>
The following are the keywords currently recognized by SQLite:
</p>

<blockquote>
<table width="100%" class="pdf_keywords">
<tr>
<td align="left" valign="top" width="20%">

<tcl>
set n [llength $keyword_list]
set nCol 5
set nRow [expr {($n+$nCol-1)/$nCol}]
set i 0
foreach word $keyword_list {
  if {[string index $word end]=="*"} {
    set word [string range $word 0 end-1]
    set font i
  } else {
    set font b
  }
  if {$i==$nRow} {
    hd_puts "</td><td valign=\"top\" align=\"left\" width=\"20%\">"
    set i 1
  } else {
    incr i
  }
  hd_puts "<$font>$word</$font><br>"
}
</tcl>
</td></tr></table></blockquote>

<h2>Special names</h2>

<p>The following are not keywords in SQLite, but are used as names of 
system objects.  They can be used as an identifier for a different 
type of object.</p>

<blockquote class="pdf_keywords"><b>
  _ROWID_<br>
  MAIN<br>
  OID<br>
  ROWID<br>
  SQLITE_MASTER<br>
  SQLITE_SEQUENCE<br>
  SQLITE_TEMP_MASTER<br>
  TEMP<br>
</b></blockquote>
