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<!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN" "http://www.w3.org/TR/html4/loose.dtd"> <HTML ><HEAD ><TITLE >SET CONSTRAINTS</TITLE ><META NAME="GENERATOR" CONTENT="Modular DocBook HTML Stylesheet Version 1.79"><LINK REV="MADE" HREF="mailto:pgsql-docs@postgresql.org"><LINK REL="HOME" TITLE="PostgreSQL 9.2.24 Documentation" HREF="index.html"><LINK REL="UP" TITLE="SQL Commands" HREF="sql-commands.html"><LINK REL="PREVIOUS" TITLE="SET" HREF="sql-set.html"><LINK REL="NEXT" TITLE="SET ROLE" HREF="sql-set-role.html"><LINK REL="STYLESHEET" TYPE="text/css" HREF="stylesheet.css"><META HTTP-EQUIV="Content-Type" CONTENT="text/html; charset=ISO-8859-1"><META NAME="creation" CONTENT="2017-11-06T22:43:11"></HEAD ><BODY CLASS="REFENTRY" ><DIV CLASS="NAVHEADER" ><TABLE SUMMARY="Header navigation table" WIDTH="100%" BORDER="0" CELLPADDING="0" CELLSPACING="0" ><TR ><TH COLSPAN="5" ALIGN="center" VALIGN="bottom" ><A HREF="index.html" >PostgreSQL 9.2.24 Documentation</A ></TH ></TR ><TR ><TD WIDTH="10%" ALIGN="left" VALIGN="top" ><A TITLE="SET" HREF="sql-set.html" ACCESSKEY="P" >Prev</A ></TD ><TD WIDTH="10%" ALIGN="left" VALIGN="top" ><A HREF="sql-commands.html" ACCESSKEY="U" >Up</A ></TD ><TD WIDTH="60%" ALIGN="center" VALIGN="bottom" ></TD ><TD WIDTH="20%" ALIGN="right" VALIGN="top" ><A TITLE="SET ROLE" HREF="sql-set-role.html" ACCESSKEY="N" >Next</A ></TD ></TR ></TABLE ><HR ALIGN="LEFT" WIDTH="100%"></DIV ><H1 ><A NAME="SQL-SET-CONSTRAINTS" ></A >SET CONSTRAINTS</H1 ><DIV CLASS="REFNAMEDIV" ><A NAME="AEN78865" ></A ><H2 >Name</H2 >SET CONSTRAINTS -- set constraint check timing for the current transaction</DIV ><DIV CLASS="REFSYNOPSISDIV" ><A NAME="AEN78870" ></A ><H2 >Synopsis</H2 ><PRE CLASS="SYNOPSIS" >SET CONSTRAINTS { ALL | <TT CLASS="REPLACEABLE" ><I >name</I ></TT > [, ...] } { DEFERRED | IMMEDIATE }</PRE ></DIV ><DIV CLASS="REFSECT1" ><A NAME="AEN78873" ></A ><H2 >Description</H2 ><P > <TT CLASS="COMMAND" >SET CONSTRAINTS</TT > sets the behavior of constraint checking within the current transaction. <TT CLASS="LITERAL" >IMMEDIATE</TT > constraints are checked at the end of each statement. <TT CLASS="LITERAL" >DEFERRED</TT > constraints are not checked until transaction commit. Each constraint has its own <TT CLASS="LITERAL" >IMMEDIATE</TT > or <TT CLASS="LITERAL" >DEFERRED</TT > mode. </P ><P > Upon creation, a constraint is given one of three characteristics: <TT CLASS="LITERAL" >DEFERRABLE INITIALLY DEFERRED</TT >, <TT CLASS="LITERAL" >DEFERRABLE INITIALLY IMMEDIATE</TT >, or <TT CLASS="LITERAL" >NOT DEFERRABLE</TT >. The third class is always <TT CLASS="LITERAL" >IMMEDIATE</TT > and is not affected by the <TT CLASS="COMMAND" >SET CONSTRAINTS</TT > command. The first two classes start every transaction in the indicated mode, but their behavior can be changed within a transaction by <TT CLASS="COMMAND" >SET CONSTRAINTS</TT >. </P ><P > <TT CLASS="COMMAND" >SET CONSTRAINTS</TT > with a list of constraint names changes the mode of just those constraints (which must all be deferrable). Each constraint name can be schema-qualified. The current schema search path is used to find the first matching name if no schema name is specified. <TT CLASS="COMMAND" >SET CONSTRAINTS ALL</TT > changes the mode of all deferrable constraints. </P ><P > When <TT CLASS="COMMAND" >SET CONSTRAINTS</TT > changes the mode of a constraint from <TT CLASS="LITERAL" >DEFERRED</TT > to <TT CLASS="LITERAL" >IMMEDIATE</TT >, 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 <TT CLASS="COMMAND" >SET CONSTRAINTS</TT > command. If any such constraint is violated, the <TT CLASS="COMMAND" >SET CONSTRAINTS</TT > fails (and does not change the constraint mode). Thus, <TT CLASS="COMMAND" >SET CONSTRAINTS</TT > can be used to force checking of constraints to occur at a specific point in a transaction. </P ><P > Currently, only <TT CLASS="LITERAL" >UNIQUE</TT >, <TT CLASS="LITERAL" >PRIMARY KEY</TT >, <TT CLASS="LITERAL" >REFERENCES</TT > (foreign key), and <TT CLASS="LITERAL" >EXCLUDE</TT > constraints are affected by this setting. <TT CLASS="LITERAL" >NOT NULL</TT > and <TT CLASS="LITERAL" >CHECK</TT > constraints are always checked immediately when a row is inserted or modified (<SPAN CLASS="emphasis" ><I CLASS="EMPHASIS" >not</I ></SPAN > at the end of the statement). Uniqueness and exclusion constraints that have not been declared <TT CLASS="LITERAL" >DEFERRABLE</TT > are also checked immediately. </P ><P > The firing of triggers that are declared as <SPAN CLASS="QUOTE" >"constraint triggers"</SPAN > is also controlled by this setting — they fire at the same time that the associated constraint should be checked. </P ></DIV ><DIV CLASS="REFSECT1" ><A NAME="AEN78909" ></A ><H2 >Notes</H2 ><P > Because <SPAN CLASS="PRODUCTNAME" >PostgreSQL</SPAN > does not require constraint names to be unique within a schema (but only per-table), it is possible that there is more than one match for a specified constraint name. In this case <TT CLASS="COMMAND" >SET CONSTRAINTS</TT > will act on all matches. For a non-schema-qualified name, once a match or matches have been found in some schema in the search path, schemas appearing later in the path are not searched. </P ><P > This command only alters the behavior of constraints within the current transaction. Thus, if you execute this command outside of a transaction block (<TT CLASS="COMMAND" >BEGIN</TT >/<TT CLASS="COMMAND" >COMMIT</TT > pair), it will not appear to have any effect. </P ></DIV ><DIV CLASS="REFSECT1" ><A NAME="AEN78917" ></A ><H2 >Compatibility</H2 ><P > This command complies with the behavior defined in the SQL standard, except for the limitation that, in <SPAN CLASS="PRODUCTNAME" >PostgreSQL</SPAN >, it does not apply to <TT CLASS="LITERAL" >NOT NULL</TT > and <TT CLASS="LITERAL" >CHECK</TT > constraints. Also, <SPAN CLASS="PRODUCTNAME" >PostgreSQL</SPAN > checks non-deferrable uniqueness constraints immediately, not at end of statement as the standard would suggest. </P ></DIV ><DIV CLASS="NAVFOOTER" ><HR ALIGN="LEFT" WIDTH="100%"><TABLE SUMMARY="Footer navigation table" WIDTH="100%" BORDER="0" CELLPADDING="0" CELLSPACING="0" ><TR ><TD WIDTH="33%" ALIGN="left" VALIGN="top" ><A HREF="sql-set.html" ACCESSKEY="P" >Prev</A ></TD ><TD WIDTH="34%" ALIGN="center" VALIGN="top" ><A HREF="index.html" ACCESSKEY="H" >Home</A ></TD ><TD WIDTH="33%" ALIGN="right" VALIGN="top" ><A HREF="sql-set-role.html" ACCESSKEY="N" >Next</A ></TD ></TR ><TR ><TD WIDTH="33%" ALIGN="left" VALIGN="top" >SET</TD ><TD WIDTH="34%" ALIGN="center" VALIGN="top" ><A HREF="sql-commands.html" ACCESSKEY="U" >Up</A ></TD ><TD WIDTH="33%" ALIGN="right" VALIGN="top" >SET ROLE</TD ></TR ></TABLE ></DIV ></BODY ></HTML >