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
"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();