lang.tcl

sqlite-3.4.1,嵌入式数据库.是一个功能强大的开源数据库,给学习和研发以及小型公司的发展带来了全所未有的好处.

<p>At this time SQLite supports only FOR EACH ROW triggers, not FOR EACH
STATEMENT triggers. Hence explicitly specifying FOR EACH ROW is optional.  FOR
EACH ROW implies that the SQL statements specified as <i>trigger-steps</i> 
may be executed (depending on the WHEN clause) for each database row being
inserted, updated or deleted by the statement causing the trigger to fire.</p>

<p>Both the WHEN clause and the <i>trigger-steps</i> may access elements of 
the row being inserted, deleted or updated using references of the form 
"NEW.<i>column-name</i>" and "OLD.<i>column-name</i>", where
<i>column-name</i> is the name of a column from the table that the trigger
is associated with. OLD and NEW references may only be used in triggers on
<i>trigger-event</i>s for which they are relevant, as follows:</p>

<table border=0 cellpadding=10>
<tr>
<td valign="top" align="right" width=120><i>INSERT</i></td>
<td valign="top">NEW references are valid</td>
</tr>
<tr>
<td valign="top" align="right" width=120><i>UPDATE</i></td>
<td valign="top">NEW and OLD references are valid</td>
</tr>
<tr>
<td valign="top" align="right" width=120><i>DELETE</i></td>
<td valign="top">OLD references are valid</td>
</tr>
</table>
</p>

<p>If a WHEN clause is supplied, the SQL statements specified as <i>trigger-steps</i> are only executed for rows for which the WHEN clause is true. If no WHEN clause is supplied, the SQL statements are executed for all rows.</p>

<p>The specified <i>trigger-time</i> determines when the <i>trigger-steps</i>
will be executed relative to the insertion, modification or removal of the
associated row.</p>

<p>An ON CONFLICT clause may be specified as part of an UPDATE or INSERT
<i>trigger-step</i>. However if an ON CONFLICT clause is specified as part of 
the statement causing the trigger to fire, then this conflict handling
policy is used instead.</p>

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

<p>Triggers may be created on views, as well as ordinary tables, by specifying
INSTEAD OF in the CREATE TRIGGER statement. If one or more ON INSERT, ON DELETE
or ON UPDATE triggers are defined on a view, then it is not an error to execute
an INSERT, DELETE or UPDATE statement on the view, respectively. Thereafter,
executing an INSERT, DELETE or UPDATE on the view causes the associated
  triggers to fire. The real tables underlying the view are not modified
  (except possibly explicitly, by a trigger program).</p>

<p><b>Example:</b></p>

<p>Assuming that customer records are stored in the "customers" table, and
that order records are stored in the "orders" table, the following trigger
ensures that all associated orders are redirected when a customer changes
his or her address:</p>
}
Example {
CREATE TRIGGER update_customer_address UPDATE OF address ON customers 
  BEGIN
    UPDATE orders SET address = new.address WHERE customer_name = old.name;
  END;
}
puts {
<p>With this trigger installed, executing the statement:</p>
}

Example {
UPDATE customers SET address = '1 Main St.' WHERE name = 'Jack Jones';
}
puts {
<p>causes the following to be automatically executed:</p>
}
Example {
UPDATE orders SET address = '1 Main St.' WHERE customer_name = 'Jack Jones';
}

puts {
<p>Note that currently, triggers may behave oddly when created on tables
  with INTEGER PRIMARY KEY fields. If a BEFORE trigger program modifies the 
  INTEGER PRIMARY KEY field of a row that will be subsequently updated by the
  statement that causes the trigger to fire, then the update may not occur. 
  The workaround is to declare the table with a PRIMARY KEY column instead
  of an INTEGER PRIMARY KEY column.</p>
}

puts {
<p>A special SQL function RAISE() may be used within a trigger-program, with the following syntax</p> 
}
Syntax {raise-function} {
RAISE ( ABORT, <error-message> ) | 
RAISE ( FAIL, <error-message> ) | 
RAISE ( ROLLBACK, <error-message> ) | 
RAISE ( IGNORE )
}
puts {
<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 user, along with the specified error message.</p>

<p>When RAISE(IGNORE) is called, the remainder of the current trigger program,
the statement that caused the trigger program to execute and any subsequent
    trigger programs that would of been executed are abandoned. No database
    changes are rolled back.  If the statement that caused the trigger program
    to execute is itself part of a trigger program, then that trigger program
    resumes execution at the beginning of the next step.
</p>

<p>Triggers are removed using the <a href="#droptrigger">DROP TRIGGER</a>
statement.</p>
}


Section {CREATE VIEW} {createview}

Syntax {sql-command} {
CREATE [TEMP | TEMPORARY] VIEW [IF NOT EXISTS] [<database-name>.] <view-name> AS <select-statement>
}

puts {
<p>The CREATE VIEW command assigns a name to a pre-packaged 
<a href="#select">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 COPY, DELETE, INSERT or UPDATE a view.  Views are read-only 
in SQLite.  However, in many cases you can use a <a href="#createtrigger">
TRIGGER</a> on the view to accomplish the same thing.  Views are removed 
with the <a href="#dropview">DROP VIEW</a> 
command.</p>
}

Section {CREATE VIRTUAL TABLE} {createvtab}

Syntax {sql-command} {
CREATE VIRTUAL TABLE [<database-name> .] <table-name> USING <module-name> [( <arguments> )]
}

puts {
<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 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
<a href="capi3ref.html#sqlite3_create_module">sqlite3_create_module</a>
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
<a href="#createtable">CREATE TABLE</a> statement.  
SQLite passes the module arguments directly
to the module without any interpretation.  It is the responsibility
of the module implementation to parse and interpret its own arguments.</p>

<p>A virtual table is destroyed using the ordinary
<a href="#droptable">DROP TABLE</a> statement.  There is no
DROP VIRTUAL TABLE statement.</p>
}

Section DELETE delete

Syntax {sql-statement} {
DELETE FROM [<database-name> .] <table-name> [WHERE <expr>]
}

puts {
<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>
}


Section {DETACH DATABASE} detach

Syntax {sql-command} {
DETACH [DATABASE] <database-name>
}

puts {
<p>This statement detaches an additional database connection previously 
attached using the <a href="#attach">ATTACH DATABASE</a> 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>
}


Section {DROP INDEX} dropindex

Syntax {sql-command} {
DROP INDEX [IF EXISTS] [<database-name> .] <index-name>
}

puts {
<p>The DROP INDEX statement removes an index added
with the <a href="#createindex">
CREATE INDEX</a> 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 INSERTs.  To 
remove free space in the database, use the <a href="#vacuum">VACUUM</a> 
command.  If AUTOVACUUM mode is enabled for a database then space
will be freed automatically by DROP INDEX.</p>
}


Section {DROP TABLE} droptable

Syntax {sql-command} {
DROP TABLE [IF EXISTS] [<database-name>.] <table-name>
}

puts {
<p>The DROP TABLE statement removes a table added with the <a href=
"#createtable">CREATE TABLE</a> 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 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 INSERTs.  To 
remove free space in the database, use the <a href="#vacuum">VACUUM</a> 
command.  If AUTOVACUUM 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>
}


Section {DROP TRIGGER} droptrigger
Syntax {sql-statement} {
DROP TRIGGER [IF EXISTS] [<database-name> .] <trigger-name>
}
puts { 
<p>The DROP TRIGGER statement removes a trigger created by the 
<a href="#createtrigger">CREATE TRIGGER</a> statement.  The trigger is 
deleted from the database schema. Note that triggers are automatically 
dropped when the associated table is dropped.</p>
}


Section {DROP VIEW} dropview

Syntax {sql-command} {
DROP VIEW [IF EXISTS] <view-name>
}

puts {
<p>The DROP VIEW statement removes a view created by the <a href=
"#createview">CREATE VIEW</a> 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>
}


Section EXPLAIN explain

Syntax {sql-statement} {
EXPLAIN <sql-statement>
}

puts {
<p>The EXPLAIN command modifier is a non-standard extension.  The
idea comes from a similar command found in PostgreSQL, but the operation
is completely different.</p>

<p>If the EXPLAIN keyword appears before any other SQLite SQL command
then instead of actually executing the command, the SQLite library will
report back the sequence of virtual machine instructions it would have
used to execute the command had the EXPLAIN keyword not been present.
For additional information about virtual machine instructions see
the <a href="arch.html">architecture description</a> or the documentation
on <a href="opcode.html">available opcodes</a> for the virtual machine.</p>
}


Section expression expr

Syntax {expr} {
<expr> <binary-op> <expr> |
<expr> [NOT] <like-op> <expr> [ESCAPE <expr>] |
<unary-op> <expr> |
( <expr> ) |
<column-name> |
<table-name> . <column-name> |
<database-name> . <table-name> . <column-name> |
<literal-value> |
<parameter> |
<function-name> ( <expr-list> | STAR ) |
<expr> ISNULL |
<expr> NOTNULL |
<expr> [NOT] BETWEEN <expr> AND <expr> |
<expr> [NOT] IN ( <value-list> ) |
<expr> [NOT] IN ( <select-statement> ) |
<expr> [NOT] IN [<database-name> .] <table-name> |
[EXISTS] ( <select-statement> ) |
CASE [<expr>] LP WHEN <expr> THEN <expr> RPPLUS [ELSE <expr>] END |
CAST ( <expr> AS <type> ) |
<expr> COLLATE <collation-name>
} {like-op} {
LIKE | GLOB | REGEXP | MATCH
}

puts {
<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>