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- <!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>37.9. 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 V1.79.1" /><link rel="prev" href="xfunc-pl.html" title="37.8. Procedural Language Functions" /><link rel="next" href="xfunc-c.html" title="37.10. 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">37.9. Internal Functions</th></tr><tr><td width="10%" align="left"><a accesskey="p" href="xfunc-pl.html" title="37.8. Procedural Language Functions">Prev</a> </td><td width="10%" align="left"><a accesskey="u" href="extend.html" title="Chapter 37. Extending SQL">Up</a></td><th width="60%" align="center">Chapter 37. 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 12.4 Documentation">Home</a></td><td width="10%" align="right"> <a accesskey="n" href="xfunc-c.html" title="37.10. 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">37.9. 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">37.8. 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"> 37.10. C-Language Functions</td></tr></table></div></body></html>
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