PL/Perl can be used to write trigger functions. In a trigger function, the hash reference $_TD contains information about the current trigger event. 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, or UNKNOWN
-
$_TD->{when}
-
When the trigger was called: BEFORE, AFTER, or UNKNOWN
-
$_TD->{level}
-
The trigger level: ROW, STATEMENT, or UNKNOWN
-
$_TD->{relid}
-
OID of the table on which the trigger fired
-
$_TD->{relname}
-
Name of the table on which the trigger fired
-
$_TD->{argc}
-
Number of arguments of the trigger function
-
@{$_TD->{args}}
-
Arguments of the trigger function. Does not exist if $_TD->{argc} is 0.
Triggers can return one of the following:
-
return;
-
Execute the statement
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"SKIP"
-
Don't execute the statement
-
"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();
