mirror of https://github.com/postgres/postgres
Alvaro Herrera
15 years ago
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<!-- |
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doc/src/sgml/ref/create_constraint.sgml |
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PostgreSQL documentation |
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--> |
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<refentry id="SQL-CREATECONSTRAINT"> |
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<refmeta> |
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<refentrytitle>CREATE CONSTRAINT TRIGGER</refentrytitle> |
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<manvolnum>7</manvolnum> |
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<refmiscinfo>SQL - Language Statements</refmiscinfo> |
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</refmeta> |
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|
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<refnamediv> |
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<refname>CREATE CONSTRAINT TRIGGER</refname> |
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<refpurpose>define a new constraint trigger</refpurpose> |
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</refnamediv> |
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<indexterm zone="sql-createconstraint"> |
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<primary>CREATE CONSTRAINT TRIGGER</primary> |
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</indexterm> |
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<refsynopsisdiv> |
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<synopsis> |
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CREATE CONSTRAINT TRIGGER <replaceable class="parameter">name</replaceable> |
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AFTER <replaceable class="parameter">event</replaceable> [ OR ... ] |
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ON <replaceable class="parameter">table_name</replaceable> |
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[ FROM <replaceable class="parameter">referenced_table_name</replaceable> ] |
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{ NOT DEFERRABLE | [ DEFERRABLE ] { INITIALLY IMMEDIATE | INITIALLY DEFERRED } } |
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FOR EACH ROW |
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[ WHEN ( <replaceable class="parameter">condition</replaceable> ) ] |
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EXECUTE PROCEDURE <replaceable class="parameter">function_name</replaceable> ( <replaceable class="parameter">arguments</replaceable> ) |
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</synopsis> |
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</refsynopsisdiv> |
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<refsect1> |
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<title>Description</title> |
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<para> |
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<command>CREATE CONSTRAINT TRIGGER</command> creates a |
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<firstterm>constraint trigger</>. This is the same as a regular trigger |
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except that the timing of the trigger firing can be adjusted using |
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<xref linkend="SQL-SET-CONSTRAINTS">. |
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Constraint triggers must be <literal>AFTER ROW</> triggers. They can |
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be fired either at the end of the statement causing the triggering event, |
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or at the end of the containing transaction; in the latter case they are |
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said to be <firstterm>deferred</>. A pending deferred-trigger firing can |
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also be forced to happen immediately by using <command>SET CONSTRAINTS</>. |
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</para> |
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</refsect1> |
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<refsect1> |
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<title>Parameters</title> |
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<variablelist> |
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<varlistentry> |
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<term><replaceable class="PARAMETER">name</replaceable></term> |
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<listitem> |
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<para> |
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The name of the constraint trigger. This is also the name to use |
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when modifying the trigger's behavior using <command>SET CONSTRAINTS</>. |
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The name cannot be schema-qualified — the trigger inherits the |
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schema of its table. |
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</para> |
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</listitem> |
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</varlistentry> |
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<varlistentry> |
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<term><replaceable class="PARAMETER">event</replaceable></term> |
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<listitem> |
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<para> |
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One of <literal>INSERT</literal>, <literal>UPDATE</literal>, or |
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<literal>DELETE</literal>; this specifies the event that will fire the |
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trigger. Multiple events can be specified using <literal>OR</literal>. |
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</para> |
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</listitem> |
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</varlistentry> |
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<varlistentry> |
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<term><replaceable class="PARAMETER">table_name</replaceable></term> |
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<listitem> |
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<para> |
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The (possibly schema-qualified) name of the table in which |
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the triggering events occur. |
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</para> |
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</listitem> |
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</varlistentry> |
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|
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<varlistentry> |
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<term><replaceable class="PARAMETER">referenced_table_name</replaceable></term> |
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<listitem> |
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<para> |
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The (possibly schema-qualified) name of another table referenced by the |
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constraint. This option is used for foreign-key constraints and is not |
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recommended for general use. |
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</para> |
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</listitem> |
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</varlistentry> |
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|
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<varlistentry> |
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<term><literal>DEFERRABLE</literal></term> |
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<term><literal>NOT DEFERRABLE</literal></term> |
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<term><literal>INITIALLY IMMEDIATE</literal></term> |
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<term><literal>INITIALLY DEFERRED</literal></term> |
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<listitem> |
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<para> |
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The default timing of the trigger. |
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See the <xref linkend="SQL-CREATETABLE"> |
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documentation for details of these constraint options. |
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</para> |
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</listitem> |
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</varlistentry> |
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|
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<varlistentry> |
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<term><replaceable class="parameter">condition</replaceable></term> |
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<listitem> |
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<para> |
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A Boolean expression that determines whether the trigger function |
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will actually be executed. This acts the same as in <xref |
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linkend="SQL-CREATETRIGGER">. |
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Note in particular that evaluation of the <literal>WHEN</> |
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condition is not deferred, but occurs immediately after the row |
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update operation is performed. If the condition does not evaluate |
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to <literal>true</> then the trigger is not queued for deferred |
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execution. |
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</para> |
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</listitem> |
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</varlistentry> |
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|
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<varlistentry> |
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<term><replaceable class="PARAMETER">function_name</replaceable></term> |
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<listitem> |
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<para> |
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The function to call when the trigger is fired. See <xref |
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linkend="SQL-CREATETRIGGER"> for |
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details. |
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</para> |
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</listitem> |
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</varlistentry> |
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|
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<varlistentry> |
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<term><replaceable class="PARAMETER">arguments</replaceable></term> |
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<listitem> |
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<para> |
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Optional argument strings to pass to the trigger function. See <xref |
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linkend="SQL-CREATETRIGGER"> for |
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details. |
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</para> |
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</listitem> |
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</varlistentry> |
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</variablelist> |
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</refsect1> |
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<refsect1> |
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<title>Compatibility</title> |
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<para> |
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<command>CREATE CONSTRAINT TRIGGER</command> is a |
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<productname>PostgreSQL</productname> extension of the <acronym>SQL</> |
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standard. |
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</para> |
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</refsect1> |
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<refsect1> |
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<title>See Also</title> |
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<simplelist type="inline"> |
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<member><xref linkend="sql-createtrigger"></member> |
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<member><xref linkend="sql-droptrigger"></member> |
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<member><xref linkend="sql-set-constraints"></member> |
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</simplelist> |
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</refsect1> |
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</refentry> |
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