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<?xml version="1.0" encoding="UTF-8" standalone="no"?>
<!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Transitional//EN" "http://www.w3.org/TR/xhtml1/DTD/xhtml1-transitional.dtd"><html xmlns="http://www.w3.org/1999/xhtml"><head><meta http-equiv="Content-Type" content="text/html; charset=UTF-8" /><title>45.1. PL/Perl Functions and Arguments</title><link rel="stylesheet" type="text/css" href="stylesheet.css" /><link rev="made" href="pgsql-docs@lists.postgresql.org" /><meta name="generator" content="DocBook XSL Stylesheets Vsnapshot" /><link rel="prev" href="plperl.html" title="Chapter 45. PL/Perl — Perl Procedural Language" /><link rel="next" href="plperl-data.html" title="45.2. Data Values in PL/Perl" /></head><body id="docContent" class="container-fluid col-10"><div class="navheader"><table width="100%" summary="Navigation header"><tr><th colspan="5" align="center">45.1. PL/Perl Functions and Arguments</th></tr><tr><td width="10%" align="left"><a accesskey="p" href="plperl.html" title="Chapter 45. PL/Perl — Perl Procedural Language">Prev</a> </td><td width="10%" align="left"><a accesskey="u" href="plperl.html" title="Chapter 45. PL/Perl — Perl Procedural Language">Up</a></td><th width="60%" align="center">Chapter 45. PL/Perl — Perl Procedural Language</th><td width="10%" align="right"><a accesskey="h" href="index.html" title="PostgreSQL 15.6 Documentation">Home</a></td><td width="10%" align="right"> <a accesskey="n" href="plperl-data.html" title="45.2. Data Values in PL/Perl">Next</a></td></tr></table><hr /></div><div class="sect1" id="PLPERL-FUNCS"><div class="titlepage"><div><div><h2 class="title" style="clear: both">45.1. PL/Perl Functions and Arguments</h2></div></div></div><p>
To create a function in the PL/Perl language, use the standard
<a class="xref" href="sql-createfunction.html" title="CREATE FUNCTION"><span class="refentrytitle">CREATE FUNCTION</span></a>
syntax:
</p><pre class="programlisting">
CREATE FUNCTION <em class="replaceable"><code>funcname</code></em> (<em class="replaceable"><code>argument-types</code></em>)
RETURNS <em class="replaceable"><code>return-type</code></em>
-- function attributes can go here
AS $$
# PL/Perl function body goes here
$$ LANGUAGE plperl;
</pre><p>
The body of the function is ordinary Perl code. In fact, the PL/Perl
glue code wraps it inside a Perl subroutine. A PL/Perl function is
called in a scalar context, so it can't return a list. You can return
non-scalar values (arrays, records, and sets) by returning a reference,
as discussed below.
</p><p>
In a PL/Perl procedure, any return value from the Perl code is ignored.
</p><p>
PL/Perl also supports anonymous code blocks called with the
<a class="xref" href="sql-do.html" title="DO"><span class="refentrytitle">DO</span></a> statement:
</p><pre class="programlisting">
DO $$
# PL/Perl code
$$ LANGUAGE plperl;
</pre><p>
An anonymous code block receives no arguments, and whatever value it
might return is discarded. Otherwise it behaves just like a function.
</p><div class="note"><h3 class="title">Note</h3><p>
The use of named nested subroutines is dangerous in Perl, especially if
they refer to lexical variables in the enclosing scope. Because a PL/Perl
function is wrapped in a subroutine, any named subroutine you place inside
one will be nested. In general, it is far safer to create anonymous
subroutines which you call via a coderef. For more information, see the
entries for <code class="literal">Variable "%s" will not stay shared</code> and
<code class="literal">Variable "%s" is not available</code> in the
<span class="citerefentry"><span class="refentrytitle">perldiag</span></span> man page, or
search the Internet for <span class="quote">“<span class="quote">perl nested named subroutine</span>”</span>.
</p></div><p>
The syntax of the <code class="command">CREATE FUNCTION</code> command requires
the function body to be written as a string constant. It is usually
most convenient to use dollar quoting (see <a class="xref" href="sql-syntax-lexical.html#SQL-SYNTAX-DOLLAR-QUOTING" title="4.1.2.4. Dollar-Quoted String Constants">Section 4.1.2.4</a>) for the string constant.
If you choose to use escape string syntax <code class="literal">E''</code>,
you must double any single quote marks (<code class="literal">'</code>) and backslashes
(<code class="literal">\</code>) used in the body of the function
(see <a class="xref" href="sql-syntax-lexical.html#SQL-SYNTAX-STRINGS" title="4.1.2.1. String Constants">Section 4.1.2.1</a>).
</p><p>
Arguments and results are handled as in any other Perl subroutine:
arguments are passed in <code class="varname">@_</code>, and a result value
is returned with <code class="literal">return</code> or as the last expression
evaluated in the function.
</p><p>
For example, a function returning the greater of two integer values
could be defined as:
</p><pre class="programlisting">
CREATE FUNCTION perl_max (integer, integer) RETURNS integer AS $$
if ($_[0] > $_[1]) { return $_[0]; }
return $_[1];
$$ LANGUAGE plperl;
</pre><p>
</p><div class="note"><h3 class="title">Note</h3><p>
Arguments will be converted from the database's encoding to UTF-8
for use inside PL/Perl, and then converted from UTF-8 back to the
database encoding upon return.
</p></div><p>
If an SQL null value<a id="id-1.8.10.9.10.1" class="indexterm"></a> is passed to a function,
the argument value will appear as <span class="quote">“<span class="quote">undefined</span>”</span> 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 <code class="literal">STRICT</code> to the function definition to make
<span class="productname">PostgreSQL</span> 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 <code class="function">perl_max</code> with
one null and one nonnull argument to return the nonnull argument,
rather than a null value:
</p><pre class="programlisting">
CREATE FUNCTION perl_max (integer, integer) RETURNS integer AS $$
my ($x, $y) = @_;
if (not defined $x) {
return undef if not defined $y;
return $y;
}
return $x if not defined $y;
return $x if $x > $y;
return $y;
$$ LANGUAGE plperl;
</pre><p>
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.
</p><p>
Anything in a function argument that is not a reference is
a string, which is in the standard <span class="productname">PostgreSQL</span>
external text representation for the relevant data type. In the case of
ordinary numeric or text types, Perl will just do the right thing and
the programmer will normally not have to worry about it. However, in
other cases the argument will need to be converted into a form that is
more usable in Perl. For example, the <code class="function">decode_bytea</code>
function can be used to convert an argument of
type <code class="type">bytea</code> into unescaped binary.
</p><p>
Similarly, values passed back to <span class="productname">PostgreSQL</span>
must be in the external text representation format. For example, the
<code class="function">encode_bytea</code> function can be used to
escape binary data for a return value of type <code class="type">bytea</code>.
</p><p>
One case that is particularly important is boolean values. As just
stated, the default behavior for <code class="type">bool</code> values is that they
are passed to Perl as text, thus either <code class="literal">'t'</code>
or <code class="literal">'f'</code>. This is problematic, since Perl will not
treat <code class="literal">'f'</code> as false! It is possible to improve matters
by using a <span class="quote">“<span class="quote">transform</span>”</span> (see
<a class="xref" href="sql-createtransform.html" title="CREATE TRANSFORM"><span class="refentrytitle">CREATE TRANSFORM</span></a>). Suitable transforms are provided
by the <code class="filename">bool_plperl</code> extension. To use it, install
the extension:
</p><pre class="programlisting">
CREATE EXTENSION bool_plperl; -- or bool_plperlu for PL/PerlU
</pre><p>
Then use the <code class="literal">TRANSFORM</code> function attribute for a
PL/Perl function that takes or returns <code class="type">bool</code>, for example:
</p><pre class="programlisting">
CREATE FUNCTION perl_and(bool, bool) RETURNS bool
TRANSFORM FOR TYPE bool
AS $$
my ($a, $b) = @_;
return $a && $b;
$$ LANGUAGE plperl;
</pre><p>
When this transform is applied, <code class="type">bool</code> arguments will be seen
by Perl as being <code class="literal">1</code> or empty, thus properly true or
false. If the function result is type <code class="type">bool</code>, it will be true
or false according to whether Perl would evaluate the returned value as
true.
Similar transformations are also performed for boolean query arguments
and results of SPI queries performed inside the function
(<a class="xref" href="plperl-builtins.html#PLPERL-DATABASE" title="45.3.1. Database Access from PL/Perl">Section 45.3.1</a>).
</p><p>
Perl can return <span class="productname">PostgreSQL</span> arrays as
references to Perl arrays. Here is an example:
</p><pre class="programlisting">
CREATE OR REPLACE function returns_array()
RETURNS text[][] AS $$
return [['a"b','c,d'],['e\\f','g']];
$$ LANGUAGE plperl;
select returns_array();
</pre><p>
</p><p>
Perl passes <span class="productname">PostgreSQL</span> arrays as a blessed
<code class="type">PostgreSQL::InServer::ARRAY</code> object. This object may be treated as an array
reference or a string, allowing for backward compatibility with Perl
code written for <span class="productname">PostgreSQL</span> versions below 9.1 to
run. For example:
</p><pre class="programlisting">
CREATE OR REPLACE FUNCTION concat_array_elements(text[]) RETURNS TEXT AS $$
my $arg = shift;
my $result = "";
return undef if (!defined $arg);
# as an array reference
for (@$arg) {
$result .= $_;
}
# also works as a string
$result .= $arg;
return $result;
$$ LANGUAGE plperl;
SELECT concat_array_elements(ARRAY['PL','/','Perl']);
</pre><p>
</p><div class="note"><h3 class="title">Note</h3><p>
Multidimensional arrays are represented as references to
lower-dimensional arrays of references in a way common to every Perl
programmer.
</p></div><p>
</p><p>
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:
</p><pre class="programlisting">
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;
</pre><p>
</p><p>
A PL/Perl function can return a composite-type result using the same
approach: return a reference to a hash that has the required attributes.
For example:
</p><pre class="programlisting">
CREATE TYPE testrowperl AS (f1 integer, f2 text, f3 text);
CREATE OR REPLACE FUNCTION perl_row() RETURNS testrowperl AS $$
return {f2 => 'hello', f1 => 1, f3 => 'world'};
$$ LANGUAGE plperl;
SELECT * FROM perl_row();
</pre><p>
Any columns in the declared result data type that are not present in the
hash will be returned as null values.
</p><p>
Similarly, output arguments of procedures can be returned as a hash
reference:
</p><pre class="programlisting">
CREATE PROCEDURE perl_triple(INOUT a integer, INOUT b integer) AS $$
my ($a, $b) = @_;
return {a => $a * 3, b => $b * 3};
$$ LANGUAGE plperl;
CALL perl_triple(5, 10);
</pre><p>
</p><p>
PL/Perl functions can also return sets of either scalar or
composite types. Usually you'll want to return rows one at a
time, both to speed up startup time and to keep from queuing up
the entire result set in memory. You can do this with
<code class="function">return_next</code> as illustrated below. Note that
after the last <code class="function">return_next</code>, you must put
either <code class="literal">return</code> or (better) <code class="literal">return
undef</code>.
</p><pre class="programlisting">
CREATE OR REPLACE FUNCTION perl_set_int(int)
RETURNS SETOF INTEGER AS $$
foreach (0..$_[0]) {
return_next($_);
}
return undef;
$$ LANGUAGE plperl;
SELECT * FROM perl_set_int(5);
CREATE OR REPLACE FUNCTION perl_set()
RETURNS SETOF testrowperl AS $$
return_next({ f1 => 1, f2 => 'Hello', f3 => 'World' });
return_next({ f1 => 2, f2 => 'Hello', f3 => 'PostgreSQL' });
return_next({ f1 => 3, f2 => 'Hello', f3 => 'PL/Perl' });
return undef;
$$ LANGUAGE plperl;
</pre><p>
For small result sets, you can return a reference to an array that
contains either scalars, references to arrays, or references to
hashes for simple types, array types, and composite types,
respectively. Here are some simple examples of returning the entire
result set as an array reference:
</p><pre class="programlisting">
CREATE OR REPLACE FUNCTION perl_set_int(int) RETURNS SETOF INTEGER AS $$
return [0..$_[0]];
$$ LANGUAGE plperl;
SELECT * FROM perl_set_int(5);
CREATE OR REPLACE FUNCTION perl_set() RETURNS SETOF testrowperl AS $$
return [
{ f1 => 1, f2 => 'Hello', f3 => 'World' },
{ f1 => 2, f2 => 'Hello', f3 => 'PostgreSQL' },
{ f1 => 3, f2 => 'Hello', f3 => 'PL/Perl' }
];
$$ LANGUAGE plperl;
SELECT * FROM perl_set();
</pre><p>
</p><p>
If you wish to use the <code class="literal">strict</code> pragma with your code you
have a few options. For temporary global use you can <code class="command">SET</code>
<code class="literal">plperl.use_strict</code> to true.
This will affect subsequent compilations of <span class="application">PL/Perl</span>
functions, but not functions already compiled in the current session.
For permanent global use you can set <code class="literal">plperl.use_strict</code>
to true in the <code class="filename">postgresql.conf</code> file.
</p><p>
For permanent use in specific functions you can simply put:
</p><pre class="programlisting">
use strict;
</pre><p>
at the top of the function body.
</p><p>
The <code class="literal">feature</code> pragma is also available to <code class="function">use</code> if your Perl is version 5.10.0 or higher.
</p></div><div class="navfooter"><hr /><table width="100%" summary="Navigation footer"><tr><td width="40%" align="left"><a accesskey="p" href="plperl.html" title="Chapter 45. PL/Perl — Perl Procedural Language">Prev</a> </td><td width="20%" align="center"><a accesskey="u" href="plperl.html" title="Chapter 45. PL/Perl — Perl Procedural Language">Up</a></td><td width="40%" align="right"> <a accesskey="n" href="plperl-data.html" title="45.2. Data Values in PL/Perl">Next</a></td></tr><tr><td width="40%" align="left" valign="top">Chapter 45. PL/Perl — Perl Procedural Language </td><td width="20%" align="center"><a accesskey="h" href="index.html" title="PostgreSQL 15.6 Documentation">Home</a></td><td width="40%" align="right" valign="top"> 45.2. Data Values in PL/Perl</td></tr></table></div></body></html>
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