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Overview
Comment:Add requirements markings and a section on the CASE expression to the SQL language documentation.
Timelines: family | ancestors | descendants | both | trunk
Files: files | file ages | folders
SHA1: ac0c9ef1a2aa8e77392c5bb94d4456f03b7de719
User & Date: drh 2009-12-12 01:14:22
Context
2009-12-12
15:32
Fix some requirements markings. Changes the evidence scanner to understand that requirement text that begins with "--" is comment, not actual requirement text. check-in: 88da6668cb user: drh tags: trunk
01:14
Add requirements markings and a section on the CASE expression to the SQL language documentation. check-in: ac0c9ef1a2 user: drh tags: trunk
2009-12-11
16:54
Remove the old-style requirements documents from the set of documentation pages generated. check-in: f259e08f31 user: drh tags: trunk
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<h1 align=center>SQL As Understood By SQLite</h1>

<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>
................................................................................
  if {$i==$lang_section_break || $i==2*$lang_section_break} {
    hd_puts "</ul></td><td valign=\"top\"><ul>"
  }
}
</tcl>
</ul></td></tr></table>

<p>The routines [sqlite3_prepare_v2()], [sqlite3_prepare()],
[sqlite3_prepare16()], [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
................................................................................

<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 column, 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>^If [foreign key constraints] are 
[foreign_keys pragma | enabled] when a table is renamed, then any
[foreign-key-clause | REFERENCES clauses] in any table (either the
table being renamed or some other table)
that refer to the table being renamed are modified to refer 
to the renamed table by its new name.

<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.
<li>^If [foreign key constraints] are [foreign_keys pragma | enabled] and
    a column with a [foreign-key-clause | REFERENCES clause]
    is added, the column must have a default value of NULL.
</ul>

<p>Note also that when adding a CHECK constraint, the CHECK constraint
is not tested against preexisting rows of the table.
This can result in a table that contains data that
is in violation of the CHECK constraint.  Future versions of SQLite might
change to validate CHECK constraints as they are added.</p>

<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 default implementation stores all statistics in a single
table named <b>sqlite_stat1</b>.  If SQLite is compiled with the
[SQLITE_ENABLE_STAT2] option, then additional histogram data is
collected and stored in <b>sqlite_stat2</b>.
Future enhancements may create
additional tables with the same name pattern except with the "1"
or "2" changed to a different digit.</p>

<p>The [DROP TABLE] command does
not work on the <b>sqlite_stat1</b> or <b>sqlite_stat2</b> tables,
but all the content of those tables can be queried using [SELECT]
and can be deleted, augmented, or modified using the [DELETE],
[INSERT], and [UPDATE] commands.
Appropriate care should be used when changing the content of the statistics
tables as invalid content can cause SQLite to select inefficient
query plans.  Generally speaking, one should not modify the content of
the statistics tables by any mechanism other than invoking the
ANALYZE command.</p>

<p>Statistics gathered by ANALYZE are <u>not</u> automatically updated as
the content of the database changes.  If the content of the database
changes significantly, or if the database schema changes, then one should
consider rerunning the ANALYZE command in order to update the statistics.</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 database-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. If
the system is not running in [shared cache mode], 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 does not require a 
<i>database-name</i> 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 when the last query finishes.
</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>Transactions created using BEGIN...COMMIT do not nest.
For nested transactions, use the [SAVEPOINT] and [RELEASE] commands.
The "TO SAVEPOINT <i>name</i>" clause of the ROLLBACK command shown
in the syntax diagram above is only applicable to [SAVEPOINT]
transactions.  An attempt to invoke the BEGIN command within
a transaction will fail with an error, regardless of whether
the transaction was started by [SAVEPOINT] or a prior BEGIN.
The COMMIT command and the ROLLBACK command without the TO clause
work the same on [SAVEPOINT] transactions as they do with transactions
started by BEGIN.</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>
An implicit transaction (a transaction that is started automatically,
not a transaction started by BEGIN) is committed automatically when
the last active statement finishes.  A statement finishes when its
prepared statement is [sqlite3_reset() | reset] or
[sqlite3_finalize() | finalized].  An open [sqlite3_blob] used for
incremental BLOB I/O counts as an unfinished statement.  The [sqlite3_blob]
finishes when it is [sqlite3_blob_close() | closed].
</p>

<p>
The explicit COMMIT command runs immediately, even if there are
pending [SELECT] statements.  However, if there are pending
write operations, the COMMIT command
will fail with a error code [SQLITE_BUSY].
</p>

<p>
An attempt to execute COMMIT might also result in an [SQLITE_BUSY] return code
if an another thread or process has 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>

<p>
The ROLLBACK will fail with an error code [SQLITE_BUSY] if there
are any pending queries.  Both read-only and read/write queries will
cause a ROLLBACK to fail.  A ROLLBACK must fail if there are pending
read operations (unlike COMMIT which can succeed) because bad things
will happen if the in-memory image of the database is changed out from under
an active query.
</p>

<p>
If [PRAGMA journal_mode] is set to OFF (thus disabling the rollback journal
file) then the behavior of the ROLLBACK command is undefined.
</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 entire 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
................................................................................
Section {SAVEPOINT} savepoint {SAVEPOINT RELEASE}

BubbleDiagram savepoint-stmt
BubbleDiagram release-stmt
BubbleDiagram rollback-stmt
</tcl>

<p>SAVEPOINTs are a method of creating transactions, similar to
[BEGIN] and [COMMIT], except that the SAVEPOINT and RELEASE commands
are named and may be nested.</p>

<p>The SAVEPOINT command starts a new transaction with a name.
The transaction names need not be unique.
A SAVEPOINT can be started either within or outside of
a [BEGIN]...[COMMIT].  When a SAVEPOINT is the outer-most savepoint
and it is not within a [BEGIN]...[COMMIT] then the behavior is the
same as BEGIN DEFERRED TRANSACTION.</p>

<p>The ROLLBACK TO command reverts the state of the database back to what
it was just after the corresponding SAVEPOINT.  Note that unlike that
plain [ROLLBACK] command (without the TO keyword) the ROLLBACK TO command
does not cancel the transaction.  Instead of cancelling the transaction,
the ROLLBACK TO command restarts the transaction again at the beginning.
All intervening SAVEPOINTs are cancelled, however.</p>

<p>The RELEASE is like a [COMMIT] for a SAVEPOINT.
The RELEASE command causes all savepoints back to and including the first
savepoint with a matching name to be removed from the transaction stack.  The
RELEASE of an inner transaction
does not cause any changes to be written to the database file; it merely
removes savepoints from the transaction stack such that it is
no longer possible to ROLLBACK TO those savepoints.
If a RELEASE command releases the outermost savepoint, so
that the transaction stack becomes empty, then RELEASE is the same
as [COMMIT].
The [COMMIT] command may used to release all savepoints and
commit the transaction even if the transaction was originally started
by a SAVEPOINT command instead of a [BEGIN] command.</p>

<p>If the savepoint-name in a RELEASE command does not match any
savepoint currently in the tranaction stack, then no savepoints are
released, the database is unchanged, and the RELEASE command returns
an error.</p>

<p>Note that an inner transaction might commit (using the RELEASE command)
but then later have its work undone by a ROLLBACK in an outer transaction.
A power failure or program crash or OS crash will cause the outer-most
transaction to rollback, undoing all changes that have occurred within
that outer transaction, even changes that have supposedly been "committed"
by the RELEASE command.  Content is not actually committed on the disk 
until the outermost transaction commits.</p>

<p>There are several ways of thinking about the RELEASE command:</p>

<ul>
<li><p>
Some people view RELEASE as the equivalent of COMMIT for a SAVEPOINT.
................................................................................
</p></li>
</ul>



<h3>Transaction Nesting Rules</h3>

<p>Transactions stack.  The last transaction started will be the first
transaction committed or rolled back.</p>

<p>The [BEGIN] command only works if the transaction stack is empty, or
in other words if there are no pending transactions.  If the transaction
stack is not empty when the [BEGIN] command is invoked, then the command
fails with an error.</p>

<p>The [COMMIT] command commits all outstanding transactions and leaves
the transaction stack empty.</p>

<p>The RELEASE command starts with the most recent addition to the
transaction stack and releases savepoints backwards 
in time until it releases a savepoint mark with a matching savepoint-name.
Prior savepoints, even savepoints with matching savepoint-names, are
unchanged.
If the RELEASE command causes the
transaction stack to become empty (if the RELEASE command releases the
outermost transaction from the stack) then the transaction commits.</p>

<p>The [ROLLBACK] command without a TO clause rolls backs all transactions
and leaves the transaction stack empty.</p>

<p>The ROLLBACK command with a TO clause rolls back transactions going
backwards in time back to the most recent SAVEPOINT with a matching name.
The SAVEPOINT with the matching name remains on the transaction stack,
but all database changes that occurred after that SAVEPOINT was created
are rolled back.  If the savepoint-name in a ROLLBACK TO command does not
match any SAVEPOINT on the stack, then the ROLLBACK command fails with an
error and leaves the state of the database unchanged.</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 entries 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.
This is one of the two possible interpretations of the SQL-92 standard
(the language in the standard is ambiguious) and is the interpretation
followed by PostgreSQL, MySQL, Firebird, and Oracle.  Informix and
Microsoft SQL Server follow the other interpretation of the standard.</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 SQLite itself and cannot appear in a CREATE TABLE statement.</p>

<p>Each column definition is the name of the column optionally followed by the
[datatype] for that column, then one or more optional column constraints.
SQLite uses [dynamic typing]; 
the datatype for the column does not restrict what data may be put
in that column.
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, a number, or a constant expression
enclosed in parentheses.
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>

<p>The PRIMARY KEY attribute normally creates a UNIQUE index on
the column or columns that are specified as the PRIMARY KEY.  The only
exception to this behavior is special [INTEGER PRIMARY KEY] column,
described below.
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>SQLite uses [dynamic typing] instead of static typing.  Except for the
special case of [INTEGER PRIMARY KEY], SQLite will allow values of any
type to be stored in any column regardless of the declared datatype of
that column.  The declared datatype is a [affinity | type affinity] that
SQLite attempts to comply with, but the operation will proceed even if
compliance is not possible.</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.
If no conflict clause is specified, the ABORT algorithm is used.
Different constraints within the same
table may have different conflict resolution algorithms.
If an [INSERT] or [UPDATE] statement specifies a conflict
resolution algorithm, then the algorithm specified on the INSERT or
UPDATE statement overrides the 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>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>hd_fragment rowid {INTEGER PRIMARY KEY} ROWID rowid</tcl>
<h3>ROWIDs and the INTEGER PRIMARY KEY</h3>

<p>Every row of every SQLite table has a 64-bit signed integer key 
that is unique within the same table.
This integer is usually called the "rowid".  The rowid is the actual key used
in the B-Tree that implements an SQLite table.  Rows are stored in
rowid order. The
rowid value can be accessed using one of the special names
"<b>ROWID</b>", "<b>OID</b>", or "<b>_ROWID_</b>".</p>


<p>
If a column is declared to be an INTEGER PRIMARY KEY, then that column is not
a "real" database column but instead becomes
an alias for the rowid.  Unlike normal SQLite columns, the rowid
must be a non-NULL integer value.  The rowid is not able to hold
floating point values, strings, BLOBs, or NULLs.</p>

<blockquote><i>
An INTEGER PRIMARY KEY column is an alias for the 64-bit signed integer rowid.
</i></blockquote>

<p>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>The special behavior of INTEGER PRIMARY KEY
is only available if the type name is exactly "INTEGER" (in any mixture
of upper and lower case.)  Other integer type names
like "INT" or "BIGINT" or "SHORT INTEGER" or "UNSIGNED INTEGER"
causes the primary key column to behave as an ordinary table column with
integer [affinity] and a unique index, not as an alias for the rowid.
The special behavior of INTEGER PRIMARY KEY is only available if the
primary key is a single column.  Multi-column primary keys do not become
aliases for the rowid.
The AUTOINCREMENT keyword only works on a column that is an alias
for the rowid.</p>

<p>Note that searches against a rowid are generally about twice as
fast as searches against any other PRIMARY KEY or indexed value.
</p>

<p><b>Goofy behavior alert:</b>  The following three declarations all cause
the column "x" be an alias for the rowid:</p>

<ul>
<li><tt>CREATE TABLE t(x INTEGER PRIMARY KEY ASC, y, z);</tt>
<li><tt>CREATE TABLE t(x INTEGER, y, z, PRIMARY KEY(x ASC));</tt>
<li><tt>CREATE TABLE t(x INTEGER, y, z, PRIMARY KEY(x DESC));</tt>
</ul>

<p>But, in contrast, the following declaration does <u>not</u> result in
"x" being an alias for the rowid:</p>

<ul>
<li><tt>CREATE TABLE t(x INTEGER PRIMARY KEY DESC, y, z);</tt>
</ul>

<p>This asymmetrical behavior is unfortunate and is really due to a bug
in the parser in early versions of SQLite.  But fixing the bug would
result in very serious backwards incompatibilities.  The SQLite developers
feel that goofy behavior in an corner case is far better than
a compatibility break, so the original behavior is retained.</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 
that are automatically performed when a specified database event
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] occurs on
on one or more specified columns of a table.</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>
................................................................................
<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 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 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 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>

<h3>Syntax Restrictions On UPDATE, DELETE, and INSERT Statements Within
    Triggers</h3>

<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.  The table to be modified must exist in the
  same database as the table or view to which the trigger is attached.
  </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>
</ul>

<tcl>hd_fragment instead_of_trigger {INSTEAD OF} {INSTEAD OF trigger}</tcl>
<h3>INSTEAD OF trigger</h3>

<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>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>

<h3>Examples</h3>

<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 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>

<tcl>hd_fragment undef_before {undefined BEFORE trigger behavior}</tcl>
<h3>Cautions On The Use Of BEFORE triggers</h3>

<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
................................................................................
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>

<h3>The RAISE() function</h3>

<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>


<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.</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()] 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>

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

BubbleDiagram delete-stmt 1
BubbleDiagram qualified-table-name
</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>

<h3>Restrictions on DELETE Statements Within CREATE TRIGGER</h3>

<p>There are additional syntax restrictions on DELETE statements that
occur within the body of a [CREATE TRIGGER] statement.  The <i>table-name</i>
must be unqualified. 
In other words, the <i>database-name</i><b>.</b> prefix
on the table name is not allowed within triggers. 
The table from which to delete must be in the same
database as the table to which the trigger is attached.</p>

<p>The INDEXED BY and NOT INDEXED clauses are not allowed on DELETE
statements within triggers.</p>

<p>The LIMIT clause (described below) is unsupported within triggers.</p>

<tcl>hd_fragment trucateopt {truncate optimization}</tcl>
<h3>The Truncate Optimization</h3>

<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 individual.
This "truncate" optimization makes the delete run much faster.
Prior to SQLite [version 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].

<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>

<h3>Use Of LIMIT</h3>

<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>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>

<p>The presence of a LIMIT clause defeats the truncate optimization
causing all rows being deleted to be visited.</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>

<p>^If [foreign key constraints] are enabled, a DROP TABLE command performs an
implicit [DELETE | DELETE FROM &lt;tbl&gt;] 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 &lt;tbl&gt; 
is executed, so this cannot cause any triggers to fire. By contrast, ^an
................................................................................
<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
................................................................................
<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>

<tcl>hd_fragment binaryops {binary operators}</tcl>
<h3>Operators</h3>
<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>IS  IN  LIKE  GLOB  MATCH  REGEXP
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>"

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 that NULL values compare
equal to one another.  [Operator IS] and [Operator {IS NOT}]
have the same precedence as [Operator =]."

<tcl>hd_fragment litvalue {literal value}</tcl>
<h3>Literal Values</h3>
<p>
A literal value is a constant of some kind.
Literal values may be integers, floating point numbers, strings,
BLOBs, or NULLs.
Scientific notation is supported for floating point literal values.
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>

<tcl>hd_fragment varparam parameter parameters {bound parameter} {bound parameters}</tcl>
<h3>Parameters</h3>
<p>
A "variable" or "parameter" token
specifies a placeholder in the expression for a literal
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>
................................................................................
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
[http://www.tcl.tk/ | 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.</p>

<tcl>hd_fragment like LIKE ESCAPE</tcl>
<h3>The LIKE and GLOB operators</h3>
<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 (\"%\") in the pattern matches any
sequence of zero or more characters in the string.  An underscore
(\"_\") 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 ASCII characters.  The
LIKE operator is case sensitive for unicode characters that are beyond
the ASCII range.  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.

<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 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 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>
<h3>The BETWEEN operator</h3>
<p>The BETWEEN operator is equivalent to a pair of comparisons.
"<i>a</i> <b>BETWEEN</b> <i>b</i> <b>AND</b> <i>c</i>" is 
equivalent to 
"<i>a</i><b>&gt;=</b><i>b</i> <b>AND</b> <i>a</i><b>&lt;=</b><i>c</i>".
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.








































<h3>Table Column Names</h3>
<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 [rowid]) 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.
The rowid can be used anywhere a regular
column can be used.</p>

<h3>Subqueries</h3>
<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 values 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>

<h3>CAST expressions</h3>
<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>

<h3>Functions</h3>
<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>}
................................................................................

<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 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> %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 
[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.
[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>

<h3>Modifiers</h3>

<p>The time string can be followed by zero or more modifiers that 
alter the date and time string.  Each modifier
is a transformation that is applied to the time string 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> 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.
Note that "&plusmn;NNN months" works by rendering the original date into
the YYYY-MM-DD format, adding the &plusmn;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
&plusmn;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 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
[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.
Due to precision limitations imposed by the implementations use
of 64-bit integers, 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 10675199167).</p>

<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" 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>

<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>These functions only work for dates between 0000-01-01 00:00:00
and 9999-12-31 23:59:59 (julidan 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. 
................................................................................
<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>

<table border=0 cellpadding=10>
<tcl>
funcdef {avg(X)} {*avg {avg() aggregate function}} {

  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 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 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)} {
  *group_concat {group_concat() aggregate function}
} {

  The result is a string which is the concatenation of
  all non-NULL values of <i>X</i>.  If parameter <i>Y</i> is present then
  is 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}} {

  Return 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.  NULL is returned if and only if there are
  no non-NULL values in the group.
}

funcdef {min(X)} {*minAggFunc *agg_min {min() aggregate function}} {

  Return 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.
  NULL is only returned 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}
} {

  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 integer overflow.
}
</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 its 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>

<p>The optional "<i>database-name</i><b>.</b>" prefix on the <i>table-name</i>
is support for top-level INSERT statements only.  The table name must be
unqualified for INSERT statements that occur within [CREATE TRIGGER] statements.
Likely, the "DEFAULT VALUES" form of the INSERT statement is support for
top-level INSERT statements only and not for INSERT statements within
triggers.
<p>

<tcl>
##############################################################################
Section {ON CONFLICT clause} conflict {{conflict clause} {ON CONFLICT}}
................................................................................
</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, [CREATE TRIGGER | delete triggers] only fire 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 an OR REPLACE resolution.  Nor is the 
[sqlite3_changes | change counter] incremented.
The exceptional behaviors defined in this paragraph 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 "[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>  

<tcl>
###############################################################################
Section SELECT select {SELECT query}
................................................................................
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 has 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
BubbleDiagram qualified-table-name
</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>

<h3>Restrictions on UPDATE Statements Within CREATE TRIGGER</h3>

<p>There are additional syntax restrictions on UPDATE statements that
occur within the body of a [CREATE TRIGGER] statement.  The <i>table-name</i>
must be unqualified. 
In other words, the <i>database-name</i><b>.</b> prefix
on the table name is not allowed within triggers. 
The table to be modified must be in the same
database as the table to which the trigger is attached.</p>

<p>The INDEXED BY and NOT INDEXED clauses are not allowed on UPDATE
statements within triggers.</p>

<p>The LIMIT clause (described below) is unsupported within triggers.</p>

<h3>Optional LIMIT and ORDER BY Clauses</h3>

<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>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 empty space will be reused the next time new information is
added to the database.  But in the meantime, the database file might
be larger than strictly necessary.  Also, frequent inserts, updates,
and deletes can cause the information in the database to become
fragmented - scrattered out all across the database file rather
than clustered together in one place.</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 
[ROWID | ROWIDs] of entries 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>

<p>The [page_size] and/or [auto_vacuum] mode of a database can be changed
by invoking the [page_size pragma] and/or [auto_vacuum pragma] and then
immediately VACUUMing the database.</p>

<tcl>
##############################################################################
Section {INDEXED BY} indexedby {{INDEXED BY} {NOT INDEXED}}

</tcl>
<p>The INDEXED BY phrase is a SQL extension found only in SQLite which can
be used to verify that the correct indices are being used on a [DELETE],
[SELECT], or [UPDATE] statement.
The INDEXED BY phrase always follows the name of a table that SQLite will
be reading.  The INDEXED BY phrase can be seen in the following syntax
diagrams:</p>

<tcl>
BubbleDiagram qualified-table-name
BubbleDiagram single-source
</tcl>

<p>The "INDEXED BY index-name" clause specifies that the named index
must be used in order to look up values on the preceding table.
If index-name 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 INTEGER PRIMARY KEY
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 preformance 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
................................................................................
<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 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>&#91;keyword&#93;</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>&#96;keyword&#96;</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 identifer.</p></li>
</ul>

<p>Programmers are cautioned not to use the two exceptions described in







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<h1 align=center>SQL As Understood By SQLite</h1>

<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 [SQL keywords] is 
also provided.  The SQL language syntax is described by
[syntax diagrams].










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

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

<tcl>
................................................................................
  if {$i==$lang_section_break || $i==2*$lang_section_break} {
    hd_puts "</ul></td><td valign=\"top\"><ul>"
  }
}
</tcl>
</ul></td></tr></table>

<p>^The routines [sqlite3_prepare_v2()], [sqlite3_prepare()],
[sqlite3_prepare16()], [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
................................................................................

<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 column, 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>^If [foreign key constraints] are 
[foreign_keys pragma | enabled] when a table is renamed, then any
[foreign-key-clause | REFERENCES clauses] in any table (either the
table being renamed or some other table)
that refer to the table being renamed are modified to refer 
to the renamed table by its new name.

<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.
<li>^If [foreign key constraints] are [foreign_keys pragma | enabled] and
    a column with a [foreign-key-clause | REFERENCES clause]
    is added, the column must have a default value of NULL.
</ul>)^

<p>^Note also that when adding a CHECK constraint, the CHECK constraint
is not tested against preexisting rows of the table.
^This can result in a table that contains data that
is in violation of the CHECK constraint.  Future versions of SQLite might
change to validate CHECK constraints as they are added.</p>

<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 default implementation stores all statistics in a single
table named <b>sqlite_stat1</b>.  ^If SQLite is compiled with the
[SQLITE_ENABLE_STAT2] option, then additional histogram data is
collected and stored in <b>sqlite_stat2</b>.
Future enhancements may create
additional tables with the same name pattern except with the "1"
or "2" changed to a different digit.</p>

<p> ^The [DROP TABLE] command does
not work on the <b>sqlite_stat1</b> or <b>sqlite_stat2</b> tables,
but all the content of those tables can be queried using [SELECT]
and can be deleted, augmented, or modified using the [DELETE],
[INSERT], and [UPDATE] commands.
Appropriate care should be used when changing the content of the statistics
tables as invalid content can cause SQLite to select inefficient
query plans.  Generally speaking, one should not modify the content of
the statistics tables by any mechanism other than invoking the
ANALYZE command.</p>

<p> ^Statistics gathered by ANALYZE are <u>not</u> automatically updated as
the content of the database changes.  If the content of the database
changes significantly, or if the database schema changes, then one should
consider rerunning the ANALYZE command in order to update the statistics.</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 database-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.  ^If
the system is not running in [shared cache mode], 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 does not require a 
<i>database-name</i> 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 when the last query finishes.
</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> ^(Transactions created using BEGIN...COMMIT do not nest.)^
^For nested transactions, use the [SAVEPOINT] and [RELEASE] commands.
The "TO SAVEPOINT <i>name</i>" clause of the ROLLBACK command shown
in the syntax diagram above is only applicable to [SAVEPOINT]
transactions.  ^An attempt to invoke the BEGIN command within
a transaction will fail with an error, regardless of whether
the transaction was started by [SAVEPOINT] or a prior BEGIN.
^The COMMIT command and the ROLLBACK command without the TO clause
work the same on [SAVEPOINT] transactions as they do with transactions
started by BEGIN.</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 to the
filesystem.  ^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>
^(An implicit transaction (a transaction that is started automatically,
not a transaction started by BEGIN) is committed automatically when
the last active statement finishes.  A statement finishes when its
prepared statement is [sqlite3_reset() | reset] or
[sqlite3_finalize() | finalized].  An open [sqlite3_blob] used for
incremental BLOB I/O counts as an unfinished statement.  The [sqlite3_blob]
finishes when it is [sqlite3_blob_close() | closed].)^
</p>

<p>
^The explicit COMMIT command runs immediately, even if there are
pending [SELECT] statements.  ^However, if there are pending
write operations, the COMMIT command
will fail with a error code [SQLITE_BUSY].
</p>

<p>
^An attempt to execute COMMIT might also result in an [SQLITE_BUSY] return code
if an another thread or process has 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>

<p>
^The ROLLBACK will fail with an error code [SQLITE_BUSY] if there
are any pending queries.  ^Both read-only and read/write queries will
cause a ROLLBACK to fail.  A ROLLBACK must fail if there are pending
read operations (unlike COMMIT which can succeed) because bad things
will happen if the in-memory image of the database is changed out from under
an active query.
</p>

<p>
If [PRAGMA journal_mode] is set to OFF (thus disabling the rollback journal
file) then the behavior of the ROLLBACK command is undefined.
</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 entire 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
................................................................................
Section {SAVEPOINT} savepoint {SAVEPOINT RELEASE}

BubbleDiagram savepoint-stmt
BubbleDiagram release-stmt
BubbleDiagram rollback-stmt
</tcl>

<p> ^SAVEPOINTs are a method of creating transactions, similar to
[BEGIN] and [COMMIT], except that the SAVEPOINT and RELEASE commands
are named and may be nested.</p>

<p> ^The SAVEPOINT command starts a new transaction with a name.
^The transaction names need not be unique.
^(A SAVEPOINT can be started either within or outside of
a [BEGIN]...[COMMIT].)^  ^(When a SAVEPOINT is the outer-most savepoint
and it is not within a [BEGIN]...[COMMIT] then the behavior is the
same as BEGIN DEFERRED TRANSACTION.)^</p>

<p>^The ROLLBACK TO command reverts the state of the database back to what
it was just after the corresponding SAVEPOINT.  ^Note that unlike that
plain [ROLLBACK] command (without the TO keyword) the ROLLBACK TO command
does not cancel the transaction.  ^Instead of cancelling the transaction,
the ROLLBACK TO command restarts the transaction again at the beginning.
^All intervening SAVEPOINTs are cancelled, however.</p>

<p>^The RELEASE command is like a [COMMIT] for a SAVEPOINT.
^The RELEASE command causes all savepoints back to and including the 
most recent savepoint with a matching name to be removed from the 
transaction stack.  ^The RELEASE of an inner transaction
does not cause any changes to be written to the database file; it merely
removes savepoints from the transaction stack such that it is
no longer possible to ROLLBACK TO those savepoints.
^If a RELEASE command releases the outermost savepoint, so
that the transaction stack becomes empty, then RELEASE is the same
as [COMMIT].
^The [COMMIT] command may be used to release all savepoints and
commit the transaction even if the transaction was originally started
by a SAVEPOINT command instead of a [BEGIN] command.</p>

<p>^If the savepoint-name in a RELEASE command does not match any
savepoint currently in the tranaction stack, then no savepoints are
released, the database is unchanged, and the RELEASE command returns
an error.</p>

<p>^Note that an inner transaction might commit (using the RELEASE command)
but then later have its work undone by a ROLLBACK in an outer transaction.
^A power failure or program crash or OS crash will cause the outer-most
transaction to rollback, undoing all changes that have occurred within
that outer transaction, even changes that have supposedly been "committed"
by the RELEASE command.  ^Content is not actually committed on the disk 
until the outermost transaction commits.</p>

<p>There are several ways of thinking about the RELEASE command:</p>

<ul>
<li><p>
Some people view RELEASE as the equivalent of COMMIT for a SAVEPOINT.
................................................................................
</p></li>
</ul>



<h3>Transaction Nesting Rules</h3>

<p>^The last transaction started will be the first
transaction committed or rolled back.</p>

<p>^The [BEGIN] command only works if the transaction stack is empty, or
in other words if there are no pending transactions.  ^If the transaction
stack is not empty when the [BEGIN] command is invoked, then the command
fails with an error.</p>

<p>^The [COMMIT] command commits all outstanding transactions and leaves
the transaction stack empty.</p>

<p>^The RELEASE command starts with the most recent addition to the
transaction stack and releases savepoints backwards 
in time until it releases a savepoint with a matching savepoint-name.
^Prior savepoints, even savepoints with matching savepoint-names, are
unchanged.
^If the RELEASE command causes the
transaction stack to become empty (if the RELEASE command releases the
outermost transaction from the stack) then the transaction commits.</p>

<p>^The [ROLLBACK] command without a TO clause rolls backs all transactions
and leaves the transaction stack empty.</p>

<p>^The ROLLBACK command with a TO clause rolls back transactions going
backwards in time back to the most recent SAVEPOINT with a matching name.
^The SAVEPOINT with the matching name remains on the transaction stack,
but all database changes that occurred after that SAVEPOINT was created
are rolled back.  ^If the savepoint-name in a ROLLBACK TO command does not
match any SAVEPOINT on the stack, then the ROLLBACK command fails with an
error and leaves the state of the database unchanged.</p>

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

BubbleDiagram comment-syntax
</tcl>

<p>Comments are not 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.
^Comments 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 optionally following each column name defines a
collating sequence used for text entries 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.
This is one of the two possible interpretations of the SQL-92 standard
(the language in the standard is ambiguious) and is the interpretation
followed by PostgreSQL, MySQL, Firebird, and Oracle.  Informix and
Microsoft SQL Server follow the other interpretation of the standard.</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 [DROP INDEX] 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 SQLite itself and cannot normally
appear in a CREATE TABLE statement.</p>

<p>^Each column definition is the name of the column optionally followed by the
[datatype] for that column, then one or more optional column constraints.
^SQLite uses [dynamic typing]; 
the datatype for the column does not restrict what data may be put
in that column.
^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, a number, or a constant expression
enclosed in parentheses.
^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 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>

<p>^(The PRIMARY KEY attribute normally creates a UNIQUE index on
the column or columns that are specified as the PRIMARY KEY.  The only
exception to this behavior is special [INTEGER PRIMARY KEY] column,
described below.)^
^(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>^SQLite uses [dynamic typing] instead of static typing.  ^Except for the
special case of [INTEGER PRIMARY KEY], SQLite will allow values of any
type to be stored in any column regardless of the declared datatype of
that column.  ^The declared datatype is a [affinity | type affinity] that
SQLite attempts to comply with, but the operation will proceed even if
compliance is not possible.</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.
^If no conflict clause is specified, the ABORT algorithm is used.
^Different constraints within the same
table may have different conflict resolution algorithms.
^If an [INSERT] or [UPDATE] statement specifies a conflict
resolution algorithm, then the algorithm specified on the INSERT or
UPDATE statement overrides the 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>^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 [DROP TABLE] statement.  </p>


<tcl>hd_fragment rowid {INTEGER PRIMARY KEY} ROWID rowid</tcl>
<h3>ROWIDs and the INTEGER PRIMARY KEY</h3>

<p>^Every row of every SQLite table has a 64-bit signed integer key 
that is unique within the same table.
This integer is usually called the "rowid".  ^The rowid is the actual key used
in the B-Tree that implements an SQLite table.  ^Rows are stored in
rowid order. ^The
rowid value can be accessed using one of the special names
"<b>ROWID</b>", "<b>OID</b>", or "<b>_ROWID_</b>" assuming those names
are no used by other conventional table columns.</p>

<p>
^If a column is declared to be an INTEGER PRIMARY KEY, then that column is not
a "real" database column but instead becomes
an alias for the rowid.  ^Unlike normal SQLite columns, the rowid
must be a non-NULL integer value.  ^The rowid is not able to hold
floating point values, strings, BLOBs, or NULLs.</p>

<blockquote><i>
^An INTEGER PRIMARY KEY column is an alias for the 64-bit signed integer rowid.
</i></blockquote>

<p>^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>^The special behavior of INTEGER PRIMARY KEY
is only available if the type name is exactly "INTEGER" (in any mixture
of upper and lower case.)  ^Other integer type names
like "INT" or "BIGINT" or "SHORT INTEGER" or "UNSIGNED INTEGER"
causes the primary key column to behave as an ordinary table column with
integer [affinity] and a unique index, not as an alias for the rowid.
^(The special behavior of INTEGER PRIMARY KEY is only available if the
primary key is a single column.  Multi-column primary keys do not become
aliases for the rowid.)^
^The AUTOINCREMENT keyword only works on a column that is an alias
for the rowid.</p>

<p>Note that searches against a rowid are generally about twice as
fast as searches against any other PRIMARY KEY or indexed value.
</p>

<p><b>Goofy behavior alert:</b>  ^(The following three declarations all cause
the column "x" be an alias for the rowid:</p>

<ul>
<li><tt>CREATE TABLE t(x INTEGER PRIMARY KEY ASC, y, z);</tt>
<li><tt>CREATE TABLE t(x INTEGER, y, z, PRIMARY KEY(x ASC));</tt>
<li><tt>CREATE TABLE t(x INTEGER, y, z, PRIMARY KEY(x DESC));</tt>
</ul>)^

<p>But, in contrast, ^(the following declaration does <u>not</u> result in
"x" being an alias for the rowid:</p>

<ul>
<li><tt>CREATE TABLE t(x INTEGER PRIMARY KEY DESC, y, z);</tt>
</ul>)^

<p>This asymmetrical behavior is unfortunate and is really due to a bug
in the parser in early versions of SQLite.  But fixing the bug would
result in very serious backwards incompatibilities.  The SQLite developers
feel that goofy behavior in an corner case is far better than
a compatibility break, so the original behavior is retained.</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 
that are automatically performed when a specified database event
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] occurs on
on one or more specified columns of a table.</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>
................................................................................
<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 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 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 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>

<h3>Syntax Restrictions On UPDATE, DELETE, and INSERT Statements Within
    Triggers</h3>

<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.)^  ^The table to be modified must exist in the
  same database as the table or view to which the trigger is attached.
  </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>
</ul>

<tcl>hd_fragment instead_of_trigger {INSTEAD OF} {INSTEAD OF trigger}</tcl>
<h3>INSTEAD OF trigger</h3>

<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>

<h3>Examples</h3>

<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 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>)^

<tcl>hd_fragment undef_before {undefined BEFORE trigger behavior}</tcl>
<h3>Cautions On The Use Of BEFORE triggers</h3>

<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
................................................................................
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>

<h3>The RAISE() function</h3>

<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>


<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 
[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
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 on a VIEW, unless the &lt;database-name&gt; is "temp".
^If no database 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>

<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.</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()] 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>

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

BubbleDiagram delete-stmt 1
BubbleDiagram qualified-table-name
</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>

<h3>Restrictions on DELETE Statements Within CREATE TRIGGER</h3>

<p>^There are additional syntax restrictions on DELETE statements that
occur within the body of a [CREATE TRIGGER] statement.  ^The <i>table-name</i>
must be unqualified. 
^(In other words, the <i>database-name</i><b>.</b> prefix
on the table name is not allowed within triggers. )^
^The table from which to delete must be in the same
database as the table to which the trigger is attached.</p>

<p>^The INDEXED BY and NOT INDEXED clauses are not allowed on DELETE
statements within triggers.</p>

<p>^The LIMIT clause (described below) is unsupported within triggers.</p>

<tcl>hd_fragment trucateopt {truncate optimization}</tcl>
<h3>The Truncate Optimization</h3>

<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], 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].

<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>

<h3>Use Of LIMIT</h3>

<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>^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 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 determined by the ORDER BY clause.</p>

<p>^The presence of a LIMIT clause defeats the truncate optimization
causing all rows being deleted to be visited.</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 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.
^Disk space released by the DROP INDEX command is retained for use by 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.  ^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 DROP TABLE statement does not reduce the size of the database 
file in the default mode.  ^Disk space released by the DROP TABLE
command is retained for reuse by subsequent [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>

<p>^If [foreign key constraints] are enabled, a DROP TABLE command performs an
implicit [DELETE | DELETE FROM &lt;tbl&gt;] 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 &lt;tbl&gt; 
is executed, so this cannot cause any triggers to fire. By contrast, ^an
................................................................................
<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 
[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 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 exact behavior is undocumented, unspecified, and variable.</p>

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

BubbleDiagram expr 1
BubbleDiagram literal-value
................................................................................
<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>

<tcl>hd_fragment binaryops {binary operators}</tcl>
<h3>Operators</h3>
<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>IS  IN  LIKE  GLOB  MATCH  REGEXP
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>"

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 that NULL values compare
equal to one another.  ^[Operator IS] and [Operator {IS NOT}]
have the same precedence as [Operator =]."

<tcl>hd_fragment litvalue {literal value}</tcl>
<h3>Literal Values</h3>
<p>
^A literal value is a constant of some kind.
^Literal values may be integers, floating point numbers, strings,
BLOBs, or NULLs.
^Scientific notation is supported for floating point literal values.
^(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>

<tcl>hd_fragment varparam parameter parameters {bound parameter} {bound parameters}</tcl>
<h3>Parameters</h3>
<p>
A "variable" or "parameter" token
specifies a placeholder in the expression for a literal
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>
................................................................................
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
[http://www.tcl.tk/ | 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.</p>

<tcl>hd_fragment like LIKE ESCAPE</tcl>
<h3>The LIKE and GLOB operators</h3>
<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 it's lower/upper case
equivalent (i.e. case-insensitive matching).  (A bug: ^SQLite only
understands upper/lower case for ASCII characters.  ^The
LIKE operator is case sensitive for unicode characters that are beyond
the ASCII range.  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.

<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 a [application-defined SQL 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()
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>
<h3>The BETWEEN operator</h3>
<p>^(The BETWEEN operator is equivalent to a pair of comparisons.
"<i>a</i> <b>BETWEEN</b> <i>b</i> <b>AND</b> <i>c</i>" is 
equivalent to 
"<i>a</i><b>&gt;=</b><i>b</i> <b>AND</b> <i>a</i><b>&lt;=</b><i>c</i>".)^
^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 expression}</tcl>
<h3>The CASE expression</h3>
<p>^(A CASE expression consists of the CASE keyword, an optional expression
(the "base" expression), one or more WHEN...THEN clauses, an optional
ELSE clause, and a closing END keyword.)^
^If the CASE as a base expression, then that expression is evaluated once
and the result is compared to the expression in between the WHEN and THEN
keywords for the WHEN clauses moving from left to right until a match is
found or all WHEN clauses are tested.  ^As soon as a match is found,
the expression that occurs after then THEN keyword becomes the result
of the overall CASE expression.  ^None of the other expressions to the left
of the THEN expression are ever evaluated.  ^If no WHEN terms match the
base expression, then the expression in the ELSE clause is evaluated and becomes
the result of the CASE expression, or the result of the CASE is NULL if
there is no ELSE clause.</p>

<p>^If a CASE expression has no base expression, then the WHEN phrases are
examined from left to write until a WHEN phrase where the expression between
the WHEN and THEN keywords evaluates to true.  ^A NULL value is considered
false for the purposes of this test.  ^When a true WHEN expression is
discovered, the corresponding THEN expression is evaluated and becomes the
result of the overall CASE expression.  ^If no WHEN expression evaluates to
to true, then the ELSE expression becomes the result if the ELSE clause
exists, otherwise the result is NULL.</p>

<p>^The base expression is evaluated exactly once.
^WHEN expressions are evaluated from left to write until a match is
found.  ^WHEN expressions to the right the matching WHEN are never evaluated.
^If any WHEN expression matches, its THEN expression is evaluated and
becomes the result of the overall CASE expression.  ^No THEN expression
is evaluated except the one THEN expression that corresponds to a
matching WHEN.  ^The ELSE expression is only evaluated if no WHEN
expression match.</p>

<p>^If the base expression is NULL then the result of the CASE is the
result of the ELSE expression if it exists, or NULL if the ELSE clause
is omitted.</p>


<h3>Table Column Names</h3>
<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 [rowid]) 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.
^The rowid can be used anywhere a regular
column can be used.</p>

<h3>Subqueries</h3>
<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 values 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 SELECT result contains no NULLs and if
the left operand matches any of the values in the SELECT result.
^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>

<h3>CAST expressions</h3>
<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>

<h3>Functions</h3>
<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>}
................................................................................

<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> %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 
[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.
^[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>

<h3>Modifiers</h3>

<p>^The time string can be followed by zero or more modifiers that 
alter the date and time string. ^ Each modifier
is a transformation that is applied to the time string 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> 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.
^Note that "&plusmn;NNN months" works by rendering the original date into
the YYYY-MM-DD format, adding the &plusmn;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
&plusmn;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 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
[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.
Due to precision limitations imposed by the implementations use
of 64-bit integers, 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 10675199167).</p>

<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" 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>

<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>^(These functions only work for dates between 0000-01-01 00:00:00
and 9999-12-31 23:59:59 (julidan 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. 
................................................................................
<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>

<table border=0 cellpadding=10>
<tcl>
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
  is 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.  ^NULL is returned 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.
  ^NULL is only returned 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() aggregate function
  returns 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>
</table>

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

BubbleDiagram insert-stmt 1
</tcl>

<p>The INSERT statement comes in three 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 its 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 third form of an INSERT statement is with DEFAULT VALUES.
^The INSERT ... DEFAULT VALUES statement simply creates a single new
row in the table in which each column is filled with its default value.</p>

<p>^The optional conflict-clause allows the specification of an alternative
constraint conflict resolution algorithm to use during this one INSERT 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>

<p>^The optional "<i>database-name</i><b>.</b>" prefix on the <i>table-name</i>
is support 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>

<tcl>
##############################################################################
Section {ON CONFLICT clause} conflict {{conflict clause} {ON CONFLICT}}
................................................................................
</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 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 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 when the IGNORE conflict resolution
algorithm is used.</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 following REPLACE.  
^No error is returned by the REPLACE conflict resolution.
^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, [CREATE TRIGGER | delete triggers] only fire 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 an OR REPLACE resolution.  ^Nor is the 
[sqlite3_changes | change counter] incremented.
The exceptional behaviors defined in this paragraph 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 "[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>  

<tcl>
###############################################################################
Section SELECT select {SELECT query}
................................................................................
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 has 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
BubbleDiagram qualified-table-name
</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 UPDATE command.
See the section titled
[ON CONFLICT] for additional information.</p>

<h3>Restrictions on UPDATE Statements Within CREATE TRIGGER</h3>

<p>^There are additional syntax restrictions on UPDATE statements that
occur within the body of a [CREATE TRIGGER] statement.  ^The <i>table-name</i>
of the UPDATE must be unqualified. 
^(In other words, the <i>database-name</i><b>.</b> prefix 
on the table name of the UPDATE is not allowed within triggers. 
^The table to be updated must be in the same
database as the table to which the trigger is attached.</p>

<p>^The INDEXED BY and NOT INDEXED clauses are not allowed on UPDATE
statements within triggers.</p>

<p>^The LIMIT clause for UPDATE is unsupported within triggers.</p>

<h3>Optional LIMIT and ORDER BY Clauses</h3>

<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>^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 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 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 empty space will be reused the next time new information is
added to the database.  But in the meantime, the database file might
be larger than strictly necessary.  Also, frequent inserts, updates,
and deletes can cause the information in the database to become
fragmented - scrattered out all across the database file rather
than clustered together in one place.</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 
[ROWID | ROWIDs] of entries 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>

<p>^The [page_size] and/or [auto_vacuum] mode of a database can be changed
by invoking the [page_size pragma] and/or [auto_vacuum pragma] and then
immediately VACUUMing the database.</p>

<tcl>
##############################################################################
Section {INDEXED BY} indexedby {{INDEXED BY} {NOT INDEXED}}

</tcl>
<p>^The INDEXED BY phrase is a SQL extension found only in SQLite which can
be used to verify that the correct indices are being used on a [DELETE],
[SELECT], or [UPDATE] statement.
^The INDEXED BY phrase always follows the name of a table that SQLite will
be reading.  The INDEXED BY phrase can be seen in the following syntax
diagrams:</p>

<tcl>
BubbleDiagram qualified-table-name
BubbleDiagram single-source
</tcl>

<p>^The "INDEXED BY index-name" clause specifies that the named index
must be used in order to look up values on the preceding table.
^If index-name 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 INTEGER PRIMARY KEY
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 preformance 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
................................................................................
<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 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>&#91;keyword&#93;</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>&#96;keyword&#96;</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 identifer.</p></li>
</ul>

<p>Programmers are cautioned not to use the two exceptions described in

Changes to pages/opcode.in.

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<title>SQLite Virtual Machine Opcodes</title>


<h2>SQLite Virtual Machine Opcodes</h2>

<tcl>
set fd [open $::SRC/src/vdbe.c r]
set file [read $fd]
close $fd

>







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<title>SQLite Virtual Machine Opcodes</title>
<tcl>hd_keywords {virtual machine instructions}</tcl>

<h2>SQLite Virtual Machine Opcodes</h2>

<tcl>
set fd [open $::SRC/src/vdbe.c r]
set file [read $fd]
close $fd