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<h1 class="heading">
SQL As Understood By SQLite</h1>
<h4>
CREATE TRIGGER</h4>
<p>
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<i><font color="#ff3434">sql-statement</font></i> ::=</td>
<td>
<b><font color="#2c2cf0">CREATE </font></b>[<b><font color="#2c2cf0">TEMP </font></b>
<big>|</big><b><font color="#2c2cf0"> TEMPORARY</font></b>]<b><font color="#2c2cf0">
TRIGGER </font></b><i><font color="#ff3434">trigger-name</font></i><b><font color="#2c2cf0">
</font></b>[<b><font color="#2c2cf0"> BEFORE </font></b><big>|</big><b><font color="#2c2cf0">
AFTER </font></b>]<b><font color="#2c2cf0"><br />
</font></b><i><font color="#ff3434">database-event</font></i><b><font color="#2c2cf0">
ON </font></b>[<b><font color="#2c2cf0"></font></b><i><font color="#ff3434">database-name</font></i><b><font
color="#2c2cf0"> <big>.</big></font></b>]<b><font color="#2c2cf0"> </font></b>
<i><font color="#ff3434">table-name</font></i><b><font color="#2c2cf0"><br />
</font></b><i><font color="#ff3434">trigger-action</font></i><b><font color="#2c2cf0"></font></b></td>
</tr>
</table>
<table cellpadding="10">
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<td align="right" width="1%" nowrap>
<i><font color="#ff3434">sql-statement</font></i> ::=</td>
<td>
<b><font color="#2c2cf0">CREATE </font></b>[<b><font color="#2c2cf0">TEMP </font></b>
<big>|</big><b><font color="#2c2cf0"> TEMPORARY</font></b>]<b><font color="#2c2cf0">
TRIGGER </font></b><i><font color="#ff3434">trigger-name</font></i><b><font color="#2c2cf0">
INSTEAD OF<br />
</font></b><i><font color="#ff3434">database-event</font></i><b><font color="#2c2cf0">
ON </font></b>[<b><font color="#2c2cf0"></font></b><i><font color="#ff3434">database-name</font></i><b><font
color="#2c2cf0"> <big>.</big></font></b>]<b><font color="#2c2cf0"> </font></b>
<i><font color="#ff3434">view-name</font></i><b><font color="#2c2cf0"><br />
</font></b><i><font color="#ff3434">trigger-action</font></i><b><font color="#2c2cf0"></font></b></td>
</tr>
</table>
<table cellpadding="10">
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<td align="right" width="1%" nowrap>
<i><font color="#ff3434">database-event</font></i> ::=</td>
<td>
<b><font color="#2c2cf0">DELETE </font></b><big>|</big><b><font color="#2c2cf0">
<br />
INSERT </font></b><big>|</big><b><font color="#2c2cf0">
<br />
UPDATE </font></b><big>|</big><b><font color="#2c2cf0">
<br />
UPDATE OF </font></b><i><font color="#ff3434">column-list</font></i><b><font color="#2c2cf0"></font></b></td>
</tr>
</table>
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<td align="right" width="1%" nowrap>
<i><font color="#ff3434">trigger-action</font></i> ::=</td>
<td>
<b><font color="#2c2cf0"></font></b>[<b><font color="#2c2cf0"> FOR EACH ROW </font>
</b><big>|</big><b><font color="#2c2cf0"> FOR EACH STATEMENT </font></b>]<b><font
color="#2c2cf0"> </font></b>[<b><font color="#2c2cf0"> WHEN </font></b><i><font color="#ff3434">
expression</font></i><b><font color="#2c2cf0"> </font></b>]<b><font color="#2c2cf0">
<br />
BEGIN
<br />
</font></b><i><font color="#ff3434">trigger-step</font></i><b><font
color="#2c2cf0"> ; </font></b>[<b><font color="#2c2cf0"> </font></b><i><font color="#ff3434">
trigger-step</font></i><b><font color="#2c2cf0"> ; </font></b>]<b><font color="#2c2cf0"></font></b><big>*</big><b><font
color="#2c2cf0"><br />
END</font></b></td>
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<table cellpadding="10">
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<td align="right" width="1%" nowrap>
<i><font color="#ff3434">trigger-step</font></i> ::=</td>
<td>
<b><font color="#2c2cf0"></font></b><i><font color="#ff3434">update-statement</font></i><b><font
color="#2c2cf0"> </font></b><big>|</big><b><font color="#2c2cf0"> </font></b><i><font
color="#ff3434">insert-statement</font></i><b><font color="#2c2cf0"> </font></b>
<big>|</big><b><font color="#2c2cf0">
<br />
</font></b><i><font color="#ff3434">delete-statement</font></i><b><font color="#2c2cf0">
</font></b><big>|</big><b><font color="#2c2cf0"> </font></b><i><font color="#ff3434">
select-statement</font></i><b><font color="#2c2cf0"></font></b></td>
</tr>
</table>
</p>
<p>
The CREATE TRIGGER statement is used to add triggers to the database schema. Triggers
are database operations (the <i>trigger-action</i>) that are automatically performed
when a specified database event (the <i>database-event</i>) occurs.
</p>
<p>
A trigger may be specified to fire whenever a DELETE, INSERT or UPDATE of a particular
database table occurs, or whenever an UPDATE of one or more specified columns of
a table are updated.</p>
<p>
At this time SQLite supports only FOR EACH ROW triggers, not FOR EACH STATEMENT
triggers. Hence explicitly specifying FOR EACH ROW is optional. FOR EACH ROW implies
that the SQL statements specified as <i>trigger-steps</i> may be executed (depending
on the WHEN clause) for each database row being inserted, updated or deleted by
the statement causing the trigger to fire.</p>
<p>
Both the WHEN clause and the <i>trigger-steps</i> may access elements of the row
being inserted, deleted or updated using references of the form "NEW.<i>column-name</i>"
and "OLD.<i>column-name</i>", where <i>column-name</i> is the name of a column from the table that the trigger is associated with. OLD and NEW references may only be
used in triggers on <i>trigger-event</i>s for which they are relevant, as follows:</p>
<p>
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<td align="right" valign="top" width="120">
<i>INSERT</i></td>
<td valign="top">
NEW references are valid</td>
</tr>
<tr>
<td align="right" valign="top" width="120">
<i>UPDATE</i></td>
<td valign="top">
NEW and OLD references are valid</td>
</tr>
<tr>
<td align="right" valign="top" width="120">
<i>DELETE</i></td>
<td valign="top">
OLD references are valid</td>
</tr>
</table>
</p>
<p>
</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>
<blockquote>
<pre>
CREATE TRIGGER update_customer_address UPDATE OF address ON customers
BEGIN
UPDATE orders SET address = new.address WHERE customer_name = old.name;
END;
</pre>
</blockquote>
<p>
With this trigger installed, executing the statement:</p>
<blockquote>
<pre>
UPDATE customers SET address = '1 Main St.' WHERE name = 'Jack Jones';
</pre>
</blockquote>
<p>
causes the following to be automatically executed:</p>
<blockquote>
<pre>
UPDATE orders SET address = '1 Main St.' WHERE customer_name = 'Jack Jones';
</pre>
</blockquote>
<p>
Note that currently, triggers may behave oddly when created on tables with INTEGER
PRIMARY KEY fields. If a BEFORE trigger program modifies the INTEGER PRIMARY KEY
field of a row that will be subsequently updated by the statement that causes the
trigger to fire, then the update may not occur. The workaround is to declare the
table with a PRIMARY KEY column instead of an INTEGER PRIMARY KEY column.</p>
<p>
A special SQL function RAISE() may be used within a trigger-program, with the following
syntax</p>
<p>
<table cellpadding="10">
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<td align="right" width="1%" nowrap>
<i><font color="#ff3434">raise-function</font></i> ::=</td>
<td>
<b><font color="#2c2cf0">RAISE <big>(</big> ABORT<big>,</big> </font></b><i><font
color="#ff3434">error-message</font></i><b><font color="#2c2cf0"> <big>)</big> </font>
</b><big>|</big><b><font color="#2c2cf0">
<br />
RAISE <big>(</big> FAIL<big>,</big> </font></b><i><font color="#ff3434">error-message</font></i><b><font
color="#2c2cf0"> <big>)</big> </font></b><big>|</big><b><font color="#2c2cf0">
<br />
RAISE <big>(</big> ROLLBACK<big>,</big> </font></b><i><font color="#ff3434">error-message</font></i><b><font
color="#2c2cf0"> <big>)</big> </font></b><big>|</big><b><font color="#2c2cf0">
<br />
RAISE <big>(</big> IGNORE <big>)</big></font></b></td>
</tr>
</table>
</p>
<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="lang_droptrigger.html">DROP TRIGGER</a>
statement.</p>
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