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>42.7. Event Trigger Procedures in PL/Tcl</A
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><P
>     Event trigger procedures can be written in PL/Tcl.
     <SPAN
CLASS="PRODUCTNAME"
>PostgreSQL</SPAN
> requires that a procedure that is
     to be called as an event trigger must be declared as a function with no
     arguments and a return type of <TT
CLASS="LITERAL"
>event_trigger</TT
>.
    </P
><P
>     The information from the trigger manager is passed to the procedure body
     in the following variables:

     <P
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CLASS="VARIABLELIST"
><DL
><DT
><TT
CLASS="VARNAME"
>$TG_event</TT
></DT
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>         The name of the event the trigger is fired for.
        </P
></DD
><DT
><TT
CLASS="VARNAME"
>$TG_tag</TT
></DT
><DD
><P
>         The command tag for which the trigger is fired.
        </P
></DD
></DL
></DIV
><P>
    </P
><P
>     The return value of the trigger procedure is ignored.
    </P
><P
>     Here's a little example event trigger procedure that simply raises
     a <TT
CLASS="LITERAL"
>NOTICE</TT
> message each time a supported command is
     executed:

</P><PRE
CLASS="PROGRAMLISTING"
>CREATE OR REPLACE FUNCTION tclsnitch() RETURNS event_trigger AS $$
  elog NOTICE "tclsnitch: $TG_event $TG_tag"
$$ LANGUAGE pltcl;

CREATE EVENT TRIGGER tcl_a_snitch ON ddl_command_start EXECUTE PROCEDURE tclsnitch();</PRE
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