September 26, 2024: PostgreSQL 17 Released!
Supported Versions: Current (17) / 16 / 15 / 14 / 13 / 12
Development Versions: devel
Unsupported versions: 11 / 10 / 9.6 / 9.5 / 9.4 / 9.3 / 9.2 / 9.1 / 9.0 / 8.4 / 8.3 / 8.2 / 8.1 / 8.0
This documentation is for an unsupported version of PostgreSQL.
You may want to view the same page for the current version, or one of the other supported versions listed above instead.
PostgreSQL 9.4.26 Documentation
Prev Up Chapter 42. PL/Perl - Perl Procedural Language Next

42.6. PL/Perl Triggers

PL/Perl can be used to write trigger functions. In a trigger function, the hash reference $_TD contains information about the current trigger event. $_TD is a global variable, which gets a separate local value for each invocation of the trigger. The fields of the $_TD hash reference are:

$_TD->{new}{foo}

NEW value of column foo

$_TD->{old}{foo}

OLD value of column foo

$_TD->{name}

Name of the trigger being called

$_TD->{event}

Trigger event: INSERT, UPDATE, DELETE, TRUNCATE, or UNKNOWN

$_TD->{when}

When the trigger was called: BEFORE, AFTER, INSTEAD OF, or UNKNOWN

$_TD->{level}

The trigger level: ROW, STATEMENT, or UNKNOWN

$_TD->{relid}

OID of the table on which the trigger fired

$_TD->{table_name}

Name of the table on which the trigger fired

$_TD->{relname}

Name of the table on which the trigger fired. This has been deprecated, and could be removed in a future release. Please use $_TD->{table_name} instead.

$_TD->{table_schema}

Name of the schema in which the table on which the trigger fired, is

$_TD->{argc}

Number of arguments of the trigger function

@{$_TD->{args}}

Arguments of the trigger function. Does not exist if $_TD->{argc} is 0.

Row-level triggers can return one of the following:

return;

Execute the operation

"SKIP"

Don't execute the operation

"MODIFY"

Indicates that the NEW row was modified by the trigger function

Here is an example of a trigger function, illustrating some of the above:

CREATE TABLE test (
    i int,
    v varchar
);

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

CREATE TRIGGER test_valid_id_trig
    BEFORE INSERT OR UPDATE ON test
    FOR EACH ROW EXECUTE PROCEDURE valid_id();
Prev Home Next
Trusted and Untrusted PL/Perl Up PL/Perl Event Triggers