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<!-- $Header: /cvsroot/pgsql/doc/src/sgml/ref/set_constraints.sgml,v 1.9 2003/09/22 00:16:58 petere Exp $ -->
<refentry id="SQL-SET-CONSTRAINTS">
<refmeta>
<refentrytitle id="SQL-SET-CONSTRAINTS-title">SET CONSTRAINTS</refentrytitle>
<refmiscinfo>SQL - Language Statements</refmiscinfo>
</refmeta>
<refnamediv>
<refname>SET CONSTRAINTS</refname>
<refpurpose>set the constraint mode of the current transaction</refpurpose>
</refnamediv>
<indexterm zone="sql-set-constraints">
<primary>SET CONSTRAINTS</primary>
</indexterm>
<refsynopsisdiv>
<synopsis>
SET CONSTRAINTS { ALL | <replaceable class="parameter">name</replaceable> [, ...] } { DEFERRED | IMMEDIATE }
</synopsis>
</refsynopsisdiv>
<refsect1>
<title>Description</title>
<para>
<command>SET CONSTRAINTS</command> sets the behavior of constraint
evaluation in the current transaction. In
<literal>IMMEDIATE</literal> mode, constraints are checked at the
end of each statement. In <literal>DEFERRED</literal> mode,
constraints are not checked until transaction commit.
</para>
<para>
When you change the mode of a constraint to be
<literal>IMMEDIATE</literal>, the new constraint mode takes effect
retroactively: any outstanding data modifications that would have
been checked at the end of the transaction (when using
<literal>DEFERRED</literal>) are instead checked during the
execution of the <command>SET CONSTRAINTS</command> command.
</para>
<para>
Upon creation, a constraint is always give one of three
characteristics: <literal>INITIALLY DEFERRED</literal>,
<literal>INITIALLY IMMEDIATE DEFERRABLE</literal>, or
<literal>INITIALLY IMMEDIATE NOT DEFERRABLE</literal>. The third
class is not affected by the <command>SET CONSTRAINTS</command>
command.
</para>
<para>
Currently, only foreign key constraints are affected by this
setting. Check and unique constraints are always effectively
initially immediate not deferrable.
</para>
</refsect1>
<refsect1>
<title>Notes</title>
<para>
This command only alters the behavior of constraints within the
current transaction. Thus, if you execute this command outside of a
transaction block
(<command>BEGIN</command>/<command>COMMIT</command> pair), it will
not appear to have any effect. If you wish to change the behavior
of a constraint without needing to issue a <command>SET
CONSTRAINTS</command> command in every transaction, specify
<literal>INITIALLY DEFERRED</literal> or <literal>INITIALLY
IMMEDIATE</literal> when you create the constraint.
</para>
</refsect1>
<refsect1>
<title>Compatibility</title>
<para>
This command complies with the behavior defined in the SQL
standard, except for the limitation that, in
<productname>PostgreSQL</productname>, it only applies to
foreign-key constraints.
</para>
</refsect1>
</refentry>
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