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><A
NAME="PLPERL-TRIGGERS"
>41.6. PL/Perl Triggers</A
></H1
><P
>   PL/Perl can be used to write trigger functions.  In a trigger function,
   the hash reference <TT
CLASS="VARNAME"
>$_TD</TT
> contains information about the
   current trigger event. <TT
CLASS="VARNAME"
>$_TD</TT
> is a global variable,
   which gets a separate local value for each invocation of the trigger.
   The fields of the <TT
CLASS="VARNAME"
>$_TD</TT
> hash reference are:

   <P
></P
></P><DIV
CLASS="VARIABLELIST"
><DL
><DT
><TT
CLASS="LITERAL"
>$_TD-&gt;{new}{foo}</TT
></DT
><DD
><P
>       <TT
CLASS="LITERAL"
>NEW</TT
> value of column <TT
CLASS="LITERAL"
>foo</TT
>
      </P
></DD
><DT
><TT
CLASS="LITERAL"
>$_TD-&gt;{old}{foo}</TT
></DT
><DD
><P
>       <TT
CLASS="LITERAL"
>OLD</TT
> value of column <TT
CLASS="LITERAL"
>foo</TT
>
      </P
></DD
><DT
><TT
CLASS="LITERAL"
>$_TD-&gt;{name}</TT
></DT
><DD
><P
>       Name of the trigger being called
      </P
></DD
><DT
><TT
CLASS="LITERAL"
>$_TD-&gt;{event}</TT
></DT
><DD
><P
>       Trigger event: <TT
CLASS="LITERAL"
>INSERT</TT
>, <TT
CLASS="LITERAL"
>UPDATE</TT
>,
       <TT
CLASS="LITERAL"
>DELETE</TT
>, <TT
CLASS="LITERAL"
>TRUNCATE</TT
>, or <TT
CLASS="LITERAL"
>UNKNOWN</TT
>
      </P
></DD
><DT
><TT
CLASS="LITERAL"
>$_TD-&gt;{when}</TT
></DT
><DD
><P
>       When the trigger was called: <TT
CLASS="LITERAL"
>BEFORE</TT
>,
       <TT
CLASS="LITERAL"
>AFTER</TT
>, <TT
CLASS="LITERAL"
>INSTEAD OF</TT
>, or
       <TT
CLASS="LITERAL"
>UNKNOWN</TT
>
      </P
></DD
><DT
><TT
CLASS="LITERAL"
>$_TD-&gt;{level}</TT
></DT
><DD
><P
>       The trigger level: <TT
CLASS="LITERAL"
>ROW</TT
>, <TT
CLASS="LITERAL"
>STATEMENT</TT
>, or <TT
CLASS="LITERAL"
>UNKNOWN</TT
>
      </P
></DD
><DT
><TT
CLASS="LITERAL"
>$_TD-&gt;{relid}</TT
></DT
><DD
><P
>       OID of the table on which the trigger fired
      </P
></DD
><DT
><TT
CLASS="LITERAL"
>$_TD-&gt;{table_name}</TT
></DT
><DD
><P
>       Name of the table on which the trigger fired
      </P
></DD
><DT
><TT
CLASS="LITERAL"
>$_TD-&gt;{relname}</TT
></DT
><DD
><P
>       Name of the table on which the trigger fired. This has been deprecated,
       and could be removed in a future release.
       Please use $_TD-&gt;{table_name} instead.
      </P
></DD
><DT
><TT
CLASS="LITERAL"
>$_TD-&gt;{table_schema}</TT
></DT
><DD
><P
>       Name of the schema in which the table on which the trigger fired, is
      </P
></DD
><DT
><TT
CLASS="LITERAL"
>$_TD-&gt;{argc}</TT
></DT
><DD
><P
>       Number of arguments of the trigger function
      </P
></DD
><DT
><TT
CLASS="LITERAL"
>@{$_TD-&gt;{args}}</TT
></DT
><DD
><P
>       Arguments of the trigger function.  Does not exist if <TT
CLASS="LITERAL"
>$_TD-&gt;{argc}</TT
> is 0.
      </P
></DD
></DL
></DIV
><P>
  </P
><P
>   Row-level triggers can return one of the following:

   <P
></P
></P><DIV
CLASS="VARIABLELIST"
><DL
><DT
><TT
CLASS="LITERAL"
>return;</TT
></DT
><DD
><P
>       Execute the operation
      </P
></DD
><DT
><TT
CLASS="LITERAL"
>"SKIP"</TT
></DT
><DD
><P
>       Don't execute the operation
      </P
></DD
><DT
><TT
CLASS="LITERAL"
>"MODIFY"</TT
></DT
><DD
><P
>       Indicates that the <TT
CLASS="LITERAL"
>NEW</TT
> row was modified by
       the trigger function
      </P
></DD
></DL
></DIV
><P>
  </P
><P
>   Here is an example of a trigger function, illustrating some of the
   above:
</P><PRE
CLASS="PROGRAMLISTING"
>CREATE TABLE test (
    i int,
    v varchar
);

CREATE OR REPLACE FUNCTION valid_id() RETURNS trigger AS $$
    if (($_TD-&gt;{new}{i} &gt;= 100) || ($_TD-&gt;{new}{i} &lt;= 0)) {
        return "SKIP";    # skip INSERT/UPDATE command
    } elsif ($_TD-&gt;{new}{v} ne "immortal") {
        $_TD-&gt;{new}{v} .= "(modified by trigger)";
        return "MODIFY";  # modify row and execute INSERT/UPDATE command
    } else {
        return;           # execute INSERT/UPDATE command
    }
$$ LANGUAGE plperl;

CREATE TRIGGER test_valid_id_trig
    BEFORE INSERT OR UPDATE ON test
    FOR EACH ROW EXECUTE PROCEDURE valid_id();</PRE
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