-<!-- $PostgreSQL: pgsql/doc/src/sgml/ref/set_constraints.sgml,v 1.10 2003/11/29 19:51:39 pgsql Exp $ -->
+<!-- $PostgreSQL: pgsql/doc/src/sgml/ref/set_constraints.sgml,v 1.11 2004/09/08 20:47:37 tgl Exp $ -->
<refentry id="SQL-SET-CONSTRAINTS">
<refmeta>
<refentrytitle id="SQL-SET-CONSTRAINTS-title">SET CONSTRAINTS</refentrytitle>
<refnamediv>
<refname>SET CONSTRAINTS</refname>
- <refpurpose>set the constraint mode of the current transaction</refpurpose>
+ <refpurpose>set constraint checking modes for the current transaction</refpurpose>
</refnamediv>
<indexterm zone="sql-set-constraints">
<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.
+ checking within the current transaction. <literal>IMMEDIATE</literal>
+ constraints are checked at the end of each
+ statement. <literal>DEFERRED</literal> constraints are not checked until
+ transaction commit. Each constraint has its own
+ <literal>IMMEDIATE</literal> or <literal>DEFERRED</literal> mode.
</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
+ Upon creation, a constraint is given 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.
+ command. The first two classes start every transaction in the
+ indicated mode, but their behavior can be changed within a transaction
+ by <command>SET CONSTRAINTS</command>.
+ </para>
+
+ <para>
+ <command>SET CONSTRAINTS</command> with a list of constraint names changes
+ the mode of just those constraints (which must all be deferrable). If
+ there are multiple constraints matching any given name, all are affected.
+ <command>SET CONSTRAINTS ALL</command> changes the mode of all deferrable
+ constraints.
+ </para>
+
+ <para>
+ When you change the mode of a constraint from <literal>DEFERRED</literal>
+ to <literal>IMMEDIATE</literal>, the new mode takes effect
+ retroactively: any outstanding data modifications that would have
+ been checked at the end of the transaction are instead checked during the
+ execution of the <command>SET CONSTRAINTS</command> command.
+ If any such constraint is violated, the <command>SET CONSTRAINTS</command>
+ fails (and does not change the constraint mode).
</para>
<para>
<productname>PostgreSQL</productname>, it only applies to
foreign-key constraints.
</para>
+
+ <para>
+ The SQL standard says that constraint names appearing in <command>SET
+ CONSTRAINTS</command> can be schema-qualified. This is not yet
+ supported by <productname>PostgreSQL</productname>: the names must
+ be unqualified, and all constraints matching the command will be
+ affected no matter which schema they are in.
+ </para>
</refsect1>
</refentry>