39.1. PL/Perl Functions and Arguments

To create a function in the PL/Perl language, use the standard syntax:

CREATE FUNCTION funcname (argument-types) RETURNS return-type AS '
    # PL/Perl function body
' LANGUAGE plperl;

The body of the function is ordinary Perl code.

Arguments and results are handled as in any other Perl subroutine: Arguments are passed in @_, and a result value is returned with return or as the last expression evaluated in the function.

For example, a function returning the greater of two integer values could be defined as:

CREATE FUNCTION perl_max (integer, integer) RETURNS integer AS '
    if ($_[0] > $_[1]) { return $_[0]; }
    return $_[1];
' LANGUAGE plperl;

If an SQL null value is passed to a function, the argument value will appear as "undefined" in Perl. The above function definition will not behave very nicely with null inputs (in fact, it will act as though they are zeroes). We could add STRICT to the function definition to make PostgreSQL do something more reasonable: if a null value is passed, the function will not be called at all, but will just return a null result automatically. Alternatively, we could check for undefined inputs in the function body. For example, suppose that we wanted perl_max with one null and one non-null argument to return the non-null argument, rather than a null value:

CREATE FUNCTION perl_max (integer, integer) RETURNS integer AS '
    my ($a,$b) = @_;
    if (! defined $a) {
        if (! defined $b) { return undef; }
        return $b;
    }
    if (! defined $b) { return $a; }
    if ($a > $b) { return $a; }
    return $b;
' LANGUAGE plperl;

As shown above, to return an SQL null value from a PL/Perl function, return an undefined value. This can be done whether the function is strict or not.

Composite-type arguments are passed to the function as references to hashes. The keys of the hash are the attribute names of the composite type. Here is an example:

CREATE TABLE employee (
    name text,
    basesalary integer,
    bonus integer
);

CREATE FUNCTION empcomp(employee) RETURNS integer AS '
    my ($emp) = @_;
    return $emp->{''basesalary''} + $emp->{''bonus''};
' LANGUAGE plperl;

SELECT name, empcomp(employee) FROM employee;

There is currently no support for returning a composite-type result value.