<?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>38.9. Internal Functions</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="xfunc-pl.html" title="38.8. Procedural Language Functions" /><link rel="next" href="xfunc-c.html" title="38.10. C-Language Functions" /></head><body><div xmlns="http://www.w3.org/TR/xhtml1/transitional" class="navheader"><table width="100%" summary="Navigation header"><tr><th colspan="5" align="center">38.9. Internal Functions</th></tr><tr><td width="10%" align="left"><a accesskey="p" href="xfunc-pl.html" title="38.8. Procedural Language Functions">Prev</a> </td><td width="10%" align="left"><a accesskey="u" href="extend.html" title="Chapter 38. Extending SQL">Up</a></td><th width="60%" align="center">Chapter 38. Extending <acronym xmlns="http://www.w3.org/1999/xhtml" class="acronym">SQL</acronym></th><td width="10%" align="right"><a accesskey="h" href="index.html" title="PostgreSQL 11.5 Documentation">Home</a></td><td width="10%" align="right"> <a accesskey="n" href="xfunc-c.html" title="38.10. C-Language Functions">Next</a></td></tr></table><hr></hr></div><div class="sect1" id="XFUNC-INTERNAL"><div class="titlepage"><div><div><h2 class="title" style="clear: both">38.9. Internal Functions</h2></div></div></div><a id="id-1.8.3.12.2" class="indexterm"></a><p>
Internal functions are functions written in C that have been statically
linked into the <span class="productname">PostgreSQL</span> server.
The <span class="quote">“<span class="quote">body</span>”</span> of the function definition
specifies the C-language name of the function, which need not be the
same as the name being declared for SQL use.
(For reasons of backward compatibility, an empty body
is accepted as meaning that the C-language function name is the
same as the SQL name.)
</p><p>
Normally, all internal functions present in the
server are declared during the initialization of the database cluster
(see <a class="xref" href="creating-cluster.html" title="18.2. Creating a Database Cluster">Section 18.2</a>),
but a user could use <code class="command">CREATE FUNCTION</code>
to create additional alias names for an internal function.
Internal functions are declared in <code class="command">CREATE FUNCTION</code>
with language name <code class="literal">internal</code>. For instance, to
create an alias for the <code class="function">sqrt</code> function:
</p><pre class="programlisting">
CREATE FUNCTION square_root(double precision) RETURNS double precision
AS 'dsqrt'
LANGUAGE internal
STRICT;
</pre><p>
(Most internal functions expect to be declared <span class="quote">“<span class="quote">strict</span>”</span>.)
</p><div class="note"><h3 class="title">Note</h3><p>
Not all <span class="quote">“<span class="quote">predefined</span>”</span> functions are
<span class="quote">“<span class="quote">internal</span>”</span> in the above sense. Some predefined
functions are written in SQL.
</p></div></div><div class="navfooter"><hr /><table width="100%" summary="Navigation footer"><tr><td width="40%" align="left"><a accesskey="p" href="xfunc-pl.html">Prev</a> </td><td width="20%" align="center"><a accesskey="u" href="extend.html">Up</a></td><td width="40%" align="right"> <a accesskey="n" href="xfunc-c.html">Next</a></td></tr><tr><td width="40%" align="left" valign="top">38.8. Procedural Language Functions </td><td width="20%" align="center"><a accesskey="h" href="index.html">Home</a></td><td width="40%" align="right" valign="top"> 38.10. C-Language Functions</td></tr></table></div></body></html>
