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><H1
><A
NAME="SQL-SET-CONSTRAINTS"
></A
>SET CONSTRAINTS</H1
><DIV
CLASS="REFNAMEDIV"
><A
NAME="AEN45432"
></A
><H2
>Name</H2
>SET CONSTRAINTS -- set constraint checking modes for the current transaction</DIV
><A
NAME="AEN45435"
></A
><DIV
CLASS="REFSYNOPSISDIV"
><A
NAME="AEN45437"
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><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="AEN45440"
></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). If
there are multiple constraints matching any given name, all are affected.
<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 foreign key constraints are affected by this
setting. Check and unique constraints are always effectively
not deferrable.
</P
></DIV
><DIV
CLASS="REFSECT1"
><A
NAME="AEN45466"
></A
><H2
>Notes</H2
><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="AEN45471"
></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 only applies to
foreign-key constraints.
</P
><P
> The SQL standard says that constraint names appearing in <TT
CLASS="COMMAND"
>SET
CONSTRAINTS</TT
> can be schema-qualified. This is not yet
supported by <SPAN
CLASS="PRODUCTNAME"
>PostgreSQL</SPAN
>: the names must
be unqualified, and all constraints matching the command will be
affected no matter which schema they are in.
</P
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