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<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>

 <refsynopsisdiv>
<synopsis>
SET CONSTRAINTS { ALL | <replaceable class="parameter">constraint</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 PostgreSQL, it only
   applies to foreign-key constraints.
  </para>
 </refsect1>
</refentry>

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