<!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN" "http://www.w3.org/TR/html4/loose.dtd"> <HTML ><HEAD ><TITLE >pg_aggregate</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 9.0.15 Documentation" HREF="index.html"><LINK REL="UP" TITLE="System Catalogs" HREF="catalogs.html"><LINK REL="PREVIOUS" TITLE="Overview" HREF="catalogs-overview.html"><LINK REL="NEXT" TITLE="pg_am" HREF="catalog-pg-am.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="2014-01-24T13:16:52"></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" ><A HREF="index.html" >PostgreSQL 9.0.15 Documentation</A ></TH ></TR ><TR ><TD WIDTH="10%" ALIGN="left" VALIGN="top" ><A TITLE="Overview" HREF="catalogs-overview.html" ACCESSKEY="P" >Prev</A ></TD ><TD WIDTH="10%" ALIGN="left" VALIGN="top" ><A HREF="catalogs.html" ACCESSKEY="U" >Up</A ></TD ><TD WIDTH="60%" ALIGN="center" VALIGN="bottom" >Chapter 45. System Catalogs</TD ><TD WIDTH="20%" ALIGN="right" VALIGN="top" ><A TITLE="pg_am" HREF="catalog-pg-am.html" ACCESSKEY="N" >Next</A ></TD ></TR ></TABLE ><HR ALIGN="LEFT" WIDTH="100%"></DIV ><DIV CLASS="SECT1" ><H1 CLASS="SECT1" ><A NAME="CATALOG-PG-AGGREGATE" >45.2. <TT CLASS="STRUCTNAME" >pg_aggregate</TT ></A ></H1 ><P > The catalog <TT CLASS="STRUCTNAME" >pg_aggregate</TT > stores information about aggregate functions. An aggregate function is a function that operates on a set of values (typically one column from each row that matches a query condition) and returns a single value computed from all these values. Typical aggregate functions are <CODE CLASS="FUNCTION" >sum</CODE >, <CODE CLASS="FUNCTION" >count</CODE >, and <CODE CLASS="FUNCTION" >max</CODE >. Each entry in <TT CLASS="STRUCTNAME" >pg_aggregate</TT > is an extension of an entry in <TT CLASS="STRUCTNAME" >pg_proc</TT >. The <TT CLASS="STRUCTNAME" >pg_proc</TT > entry carries the aggregate's name, input and output data types, and other information that is similar to ordinary functions. </P ><DIV CLASS="TABLE" ><A NAME="AEN78163" ></A ><P ><B >Table 45-2. <TT CLASS="STRUCTNAME" >pg_aggregate</TT > Columns</B ></P ><TABLE BORDER="1" CLASS="CALSTABLE" ><COL><COL><COL><COL><THEAD ><TR ><TH >Name</TH ><TH >Type</TH ><TH >References</TH ><TH >Description</TH ></TR ></THEAD ><TBODY ><TR ><TD ><TT CLASS="STRUCTFIELD" >aggfnoid</TT ></TD ><TD ><TT CLASS="TYPE" >regproc</TT ></TD ><TD ><TT CLASS="LITERAL" ><A HREF="catalog-pg-proc.html" ><TT CLASS="STRUCTNAME" >pg_proc</TT ></A >.oid</TT ></TD ><TD ><TT CLASS="STRUCTNAME" >pg_proc</TT > OID of the aggregate function</TD ></TR ><TR ><TD ><TT CLASS="STRUCTFIELD" >aggtransfn</TT ></TD ><TD ><TT CLASS="TYPE" >regproc</TT ></TD ><TD ><TT CLASS="LITERAL" ><A HREF="catalog-pg-proc.html" ><TT CLASS="STRUCTNAME" >pg_proc</TT ></A >.oid</TT ></TD ><TD >Transition function</TD ></TR ><TR ><TD ><TT CLASS="STRUCTFIELD" >aggfinalfn</TT ></TD ><TD ><TT CLASS="TYPE" >regproc</TT ></TD ><TD ><TT CLASS="LITERAL" ><A HREF="catalog-pg-proc.html" ><TT CLASS="STRUCTNAME" >pg_proc</TT ></A >.oid</TT ></TD ><TD >Final function (zero if none)</TD ></TR ><TR ><TD ><TT CLASS="STRUCTFIELD" >aggsortop</TT ></TD ><TD ><TT CLASS="TYPE" >oid</TT ></TD ><TD ><TT CLASS="LITERAL" ><A HREF="catalog-pg-operator.html" ><TT CLASS="STRUCTNAME" >pg_operator</TT ></A >.oid</TT ></TD ><TD >Associated sort operator (zero if none)</TD ></TR ><TR ><TD ><TT CLASS="STRUCTFIELD" >aggtranstype</TT ></TD ><TD ><TT CLASS="TYPE" >oid</TT ></TD ><TD ><TT CLASS="LITERAL" ><A HREF="catalog-pg-type.html" ><TT CLASS="STRUCTNAME" >pg_type</TT ></A >.oid</TT ></TD ><TD >Data type of the aggregate function's internal transition (state) data</TD ></TR ><TR ><TD ><TT CLASS="STRUCTFIELD" >agginitval</TT ></TD ><TD ><TT CLASS="TYPE" >text</TT ></TD ><TD > </TD ><TD > The initial value of the transition state. This is a text field containing the initial value in its external string representation. If this field is null, the transition state value starts out null. </TD ></TR ></TBODY ></TABLE ></DIV ><P > New aggregate functions are registered with the <A HREF="sql-createaggregate.html" >CREATE AGGREGATE</A > command. See <A HREF="xaggr.html" >Section 35.10</A > for more information about writing aggregate functions and the meaning of the transition functions, etc. </P ></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="catalogs-overview.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="catalog-pg-am.html" ACCESSKEY="N" >Next</A ></TD ></TR ><TR ><TD WIDTH="33%" ALIGN="left" VALIGN="top" >Overview</TD ><TD WIDTH="34%" ALIGN="center" VALIGN="top" ><A HREF="catalogs.html" ACCESSKEY="U" >Up</A ></TD ><TD WIDTH="33%" ALIGN="right" VALIGN="top" ><TT CLASS="STRUCTNAME" >pg_am</TT ></TD ></TR ></TABLE ></DIV ></BODY ></HTML >