<!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN" "http://www.w3.org/TR/html4/loose.dtd"> <HTML ><HEAD ><TITLE >Internal Functions</TITLE ><META NAME="GENERATOR" CONTENT="Modular DocBook HTML Stylesheet Version 1.79"><LINK REV="MADE" HREF="mailto:pgsql-docs@postgresql.org"><LINK REL="HOME" TITLE="PostgreSQL 8.0.11 Documentation" HREF="index.html"><LINK REL="UP" TITLE="Extending SQL" HREF="extend.html"><LINK REL="PREVIOUS" TITLE="Procedural Language Functions" HREF="xfunc-pl.html"><LINK REL="NEXT" TITLE="C-Language Functions" HREF="xfunc-c.html"><LINK REL="STYLESHEET" TYPE="text/css" HREF="stylesheet.css"><META HTTP-EQUIV="Content-Type" CONTENT="text/html; charset=ISO-8859-1"><META NAME="creation" CONTENT="2007-02-02T03:57:22"></HEAD ><BODY CLASS="SECT1" ><DIV CLASS="NAVHEADER" ><TABLE SUMMARY="Header navigation table" WIDTH="100%" BORDER="0" CELLPADDING="0" CELLSPACING="0" ><TR ><TH COLSPAN="5" ALIGN="center" VALIGN="bottom" >PostgreSQL 8.0.11 Documentation</TH ></TR ><TR ><TD WIDTH="10%" ALIGN="left" VALIGN="top" ><A HREF="xfunc-pl.html" ACCESSKEY="P" >Prev</A ></TD ><TD WIDTH="10%" ALIGN="left" VALIGN="top" ><A HREF="extend.html" >Fast Backward</A ></TD ><TD WIDTH="60%" ALIGN="center" VALIGN="bottom" >Chapter 31. Extending <ACRONYM CLASS="ACRONYM" >SQL</ACRONYM ></TD ><TD WIDTH="10%" ALIGN="right" VALIGN="top" ><A HREF="extend.html" >Fast Forward</A ></TD ><TD WIDTH="10%" ALIGN="right" VALIGN="top" ><A HREF="xfunc-c.html" ACCESSKEY="N" >Next</A ></TD ></TR ></TABLE ><HR ALIGN="LEFT" WIDTH="100%"></DIV ><DIV CLASS="SECT1" ><H1 CLASS="SECT1" ><A NAME="XFUNC-INTERNAL" >31.8. Internal Functions</A ></H1 ><A NAME="AEN29782" ></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" >"body"</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 backwards 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 (<TT CLASS="COMMAND" >initdb</TT >), but a user could use <TT CLASS="COMMAND" >CREATE FUNCTION</TT > to create additional alias names for an internal function. Internal functions are declared in <TT CLASS="COMMAND" >CREATE FUNCTION</TT > with language name <TT CLASS="LITERAL" >internal</TT >. 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" >"strict"</SPAN >.) </P ><DIV CLASS="NOTE" ><BLOCKQUOTE CLASS="NOTE" ><P ><B >Note: </B > Not all <SPAN CLASS="QUOTE" >"predefined"</SPAN > functions are <SPAN CLASS="QUOTE" >"internal"</SPAN > in the above sense. Some predefined functions are written in SQL. </P ></BLOCKQUOTE ></DIV ></DIV ><DIV CLASS="NAVFOOTER" ><HR ALIGN="LEFT" WIDTH="100%"><TABLE SUMMARY="Footer navigation table" WIDTH="100%" BORDER="0" CELLPADDING="0" CELLSPACING="0" ><TR ><TD WIDTH="33%" ALIGN="left" VALIGN="top" ><A HREF="xfunc-pl.html" ACCESSKEY="P" >Prev</A ></TD ><TD WIDTH="34%" ALIGN="center" VALIGN="top" ><A HREF="index.html" ACCESSKEY="H" >Home</A ></TD ><TD WIDTH="33%" ALIGN="right" VALIGN="top" ><A HREF="xfunc-c.html" ACCESSKEY="N" >Next</A ></TD ></TR ><TR ><TD WIDTH="33%" ALIGN="left" VALIGN="top" >Procedural Language Functions</TD ><TD WIDTH="34%" ALIGN="center" VALIGN="top" ><A HREF="extend.html" ACCESSKEY="U" >Up</A ></TD ><TD WIDTH="33%" ALIGN="right" VALIGN="top" >C-Language Functions</TD ></TR ></TABLE ></DIV ></BODY ></HTML >