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<!--
$PostgreSQL: pgsql/doc/src/sgml/ref/create_constraint.sgml,v 1.18 2007/02/10 20:43:59 tgl Exp $
PostgreSQL documentation
-->
<refentry id="SQL-CREATECONSTRAINT">
<refmeta>
<refentrytitle id="sql-createconstraint-title">CREATE CONSTRAINT TRIGGER</refentrytitle>
<refmiscinfo>SQL - Language Statements</refmiscinfo>
</refmeta>
<refnamediv>
<refname>CREATE CONSTRAINT TRIGGER</refname>
<refpurpose>define a new constraint trigger</refpurpose>
</refnamediv>
<indexterm zone="sql-createconstraint">
<primary>CREATE CONSTRAINT TRIGGER</primary>
</indexterm>
<refsynopsisdiv>
<synopsis>
CREATE CONSTRAINT TRIGGER <replaceable class="parameter">name</replaceable>
AFTER <replaceable class="parameter">event</replaceable> [ OR ... ]
ON <replaceable class="parameter">table_name</replaceable>
[ FROM <replaceable class="parameter">referenced_table_name</replaceable> ]
{ NOT DEFERRABLE | [ DEFERRABLE ] { INITIALLY IMMEDIATE | INITIALLY DEFERRED } }
FOR EACH ROW
EXECUTE PROCEDURE <replaceable class="parameter">funcname</replaceable> ( <replaceable class="parameter">arguments</replaceable> )
</synopsis>
</refsynopsisdiv>
<refsect1>
<title>Description</title>
<para>
<command>CREATE CONSTRAINT TRIGGER</command> creates a
<firstterm>constraint trigger</>. This is the same as a regular trigger
except that the timing of the trigger firing can be adjusted using
<xref linkend="SQL-SET-CONSTRAINTS" endterm="SQL-SET-CONSTRAINTS-TITLE">.
Constraint triggers must be <literal>AFTER ROW</> triggers. They can
be fired either at the end of the statement causing the triggering event,
or at the end of the containing transaction; in the latter case they are
said to be <firstterm>deferred</>. A pending deferred-trigger firing can
also be forced to happen immediately by using <command>SET CONSTRAINTS</>.
</para>
</refsect1>
<refsect1>
<title>Parameters</title>
<variablelist>
<varlistentry>
<term><replaceable class="PARAMETER">name</replaceable></term>
<listitem>
<para>
The name of the constraint trigger. This is also the name to use
when modifying the trigger's behavior using <command>SET CONSTRAINTS</>.
The name cannot be schema-qualified — the trigger inherits the
schema of its table.
</para>
</listitem>
</varlistentry>
<varlistentry>
<term><replaceable class="PARAMETER">event</replaceable></term>
<listitem>
<para>
One of <literal>INSERT</literal>, <literal>UPDATE</literal>, or
<literal>DELETE</literal>; this specifies the event that will fire the
trigger. Multiple events can be specified using <literal>OR</literal>.
</para>
</listitem>
</varlistentry>
<varlistentry>
<term><replaceable class="PARAMETER">table_name</replaceable></term>
<listitem>
<para>
The (possibly schema-qualified) name of the table in which
the triggering events occur.
</para>
</listitem>
</varlistentry>
<varlistentry>
<term><replaceable class="PARAMETER">referenced_table_name</replaceable></term>
<listitem>
<para>
The (possibly schema-qualified) name of another table referenced by the
constraint. This option is used for foreign-key constraints and is not
recommended for general use.
</para>
</listitem>
</varlistentry>
<varlistentry>
<term><literal>DEFERRABLE</literal></term>
<term><literal>NOT DEFERRABLE</literal></term>
<term><literal>INITIALLY IMMEDIATE</literal></term>
<term><literal>INITIALLY DEFERRED</literal></term>
<listitem>
<para>
The default timing of the trigger.
See the <xref linkend="SQL-CREATETABLE" endterm="SQL-CREATETABLE-TITLE">
documentation for details of these constraint options.
</para>
</listitem>
</varlistentry>
<varlistentry>
<term><replaceable class="PARAMETER">funcname</replaceable></term>
<listitem>
<para>
The function to call when the trigger is fired. See <xref
linkend="SQL-CREATETRIGGER" endterm="SQL-CREATETRIGGER-TITLE"> for
details.
</para>
</listitem>
</varlistentry>
<varlistentry>
<term><replaceable class="PARAMETER">arguments</replaceable></term>
<listitem>
<para>
Optional argument strings to pass to the trigger function. See <xref
linkend="SQL-CREATETRIGGER" endterm="SQL-CREATETRIGGER-TITLE"> for
details.
</para>
</listitem>
</varlistentry>
</variablelist>
</refsect1>
<refsect1>
<title>Compatibility</title>
<para>
<command>CREATE CONSTRAINT TRIGGER</command> is a
<productname>PostgreSQL</productname> extension of the <acronym>SQL</>
standard.
</para>
</refsect1>
<refsect1>
<title>See Also</title>
<simplelist type="inline">
<member><xref linkend="sql-createtrigger" endterm="sql-createtrigger-title"></member>
<member><xref linkend="sql-droptrigger" endterm="sql-droptrigger-title"></member>
<member><xref linkend="sql-set-constraints" endterm="sql-set-constraints-title"></member>
</simplelist>
</refsect1>
</refentry>
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