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First files for reference pages.
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Thomas G. Lockhart
300
doc/src/sgml/ref/create_aggregate.sgml
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300
doc/src/sgml/ref/create_aggregate.sgml
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<REFENTRY ID="SQL-CREATEAGGREGATE-1">
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<REFMETA>
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<REFENTRYTITLE>
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CREATE AGGREGATE
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</REFENTRYTITLE>
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<REFMISCINFO>SQL - Language Statements</REFMISCINFO>
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</REFMETA>
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<comment>This entry needs a lot of work, especially some
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usefully complex examples. Since I don't yet understand it, I
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haven't done this.</comment>
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<REFNAMEDIV>
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<REFNAME>
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CREATE AGGREGATE
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</REFNAME>
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<REFPURPOSE>
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Defines a new aggregate function
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</REFPURPOSE>
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<REFSYNOPSISDIV>
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<REFSYNOPSISDIVINFO>
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<DATE>1998-04-15</DATE>
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</REFSYNOPSISDIVINFO>
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<SYNOPSIS>
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CREATE AGGREGATE <REPLACEABLE CLASS="PARAMETER">name</REPLACEABLE> [AS]
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([ SFUNC1 = <REPLACEABLE CLASS="PARAMETER">state_transition_function1</REPLACEABLE>
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, BASETYPE = <REPLACEABLE CLASS="PARAMETER">data_type</REPLACEABLE>
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, STYPE1 = <REPLACEABLE CLASS="PARAMETER">sfunc1_return_type</REPLACEABLE> ]
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[, SFUNC2 = <REPLACEABLE CLASS="PARAMETER">state_transition_function2</REPLACEABLE>
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, STYPE2 = <REPLACEABLE CLASS="PARAMETER">sfunc2_return_type</REPLACEABLE> ]
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[, FINALFUNC = <REPLACEABLE CLASS="PARAMETER">final_function</REPLACEABLE> ]
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[, INITCOND1 = <REPLACEABLE CLASS="PARAMETER">initial_condition1</REPLACEABLE> ]
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[, INITCOND2 = <REPLACEABLE CLASS="PARAMETER">initial_condition2</REPLACEABLE> ]
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)
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</SYNOPSIS>
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<REFSECT2 ID="R2-SQL-CREATEAGGREGATE-1">
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<REFSECT2INFO>
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<DATE>1998-04-15</DATE>
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</REFSECT2INFO>
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<TITLE>
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Inputs
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</TITLE>
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<variablelist>
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<varlistentry>
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<term></term>
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<listitem>
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<PARA>
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<VARIABLELIST>
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<VARLISTENTRY>
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<TERM>
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<REPLACEABLE CLASS="PARAMETER">name</REPLACEABLE>
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</TERM>
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<LISTITEM>
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<para>
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The name of an aggregate function to create.
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</para>
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</LISTITEM>
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</varlistentry>
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<varlistentry>
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<term>
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<REPLACEABLE CLASS="PARAMETER">state_transition_function1</REPLACEABLE>
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</term>
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<listitem>
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<para>
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</para>
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</listitem>
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</varlistentry>
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<varlistentry>
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<term>
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<REPLACEABLE CLASS="PARAMETER">data_type</REPLACEABLE>
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</term>
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<listitem>
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<para>
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</para>
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</listitem>
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</varlistentry>
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<varlistentry>
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<term>
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<REPLACEABLE CLASS="PARAMETER">sfunc1_return_type</REPLACEABLE>
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</term>
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<listitem>
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<para>
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</para>
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</listitem>
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</varlistentry>
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<varlistentry>
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<term>
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<REPLACEABLE CLASS="PARAMETER">state-transition_function2</REPLACEABLE>
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</term>
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<listitem>
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<para>
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</para>
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</listitem>
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</varlistentry>
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<varlistentry>
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<term>
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<REPLACEABLE CLASS="PARAMETER">sfunc2_return_type</REPLACEABLE>
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</term>
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<listitem>
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<para>
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</para>
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</listitem>
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</varlistentry>
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<varlistentry>
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<term>
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<REPLACEABLE CLASS="PARAMETER">final_function</REPLACEABLE>
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</term>
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<listitem>
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<para>
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</para>
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</listitem>
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</varlistentry>
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<varlistentry>
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<term>
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<REPLACEABLE CLASS="PARAMETER">initial_condition1</REPLACEABLE>
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</term>
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<listitem>
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<para>
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</para>
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</listitem>
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</varlistentry>
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<varlistentry>
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<term>
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<REPLACEABLE CLASS="PARAMETER">initial_condition2</REPLACEABLE>
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</term>
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<listitem>
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<para>
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</para>
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</listitem>
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</varlistentry>
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</variablelist>
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</PARA>
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</listitem>
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</varlistentry>
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</variablelist>
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</REFSECT2>
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<REFSECT2 ID="R2-SQL-CREATEAGGREGATE-2">
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<REFSECT2INFO>
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<DATE>1998-04-15</DATE>
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</REFSECT2INFO>
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<TITLE>
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Outputs
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</TITLE>
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<PARA>
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</PARA>
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<VARIABLELIST>
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<VARLISTENTRY>
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<TERM>
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</TERM>
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<LISTITEM>
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<PARA>
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<VARIABLELIST>
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<VARLISTENTRY>
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<TERM>
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<ReturnValue>CREATE</ReturnValue>
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</TERM>
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<LISTITEM>
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<PARA>
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Message returned if the command completes successfully.
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</PARA>
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</LISTITEM>
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</VARLISTENTRY>
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</VARIABLELIST>
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</LISTITEM>
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</VARLISTENTRY>
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</VARIABLELIST>
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</REFSECT2>
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</REFSYNOPSISDIV>
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<REFSECT1 ID="R1-SQL-CREATEAGGREGATE-1">
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<REFSECT1INFO>
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<DATE>1998-04-15</DATE>
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</REFSECT1INFO>
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<TITLE>
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Description
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</TITLE>
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<PARA>
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An aggregate function can use up to three functions, two
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state transition functions, X1 and X2:
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X1( internal-state1, next-data_item ) ---> next-internal-state1
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X2( internal-state2 ) ---> next-internal-state2
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and a final calculation function, F:
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F(internal-state1, internal-state2) ---> aggregate-value
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These functions are required to have the following properties:
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<itemizedlist>
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<listitem>
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<para>
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The arguments to state-transition-function-1 must
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be (stype1,basetype), and its return value must be
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stype1.
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</para>
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</listitem>
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<listitem>
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<para>
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The argument and return value of state-transition-
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function-2 must be stype2.
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</para>
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</listitem>
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<listitem>
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<para>
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The arguments to the final-calculation-function
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must be (stype1,stype2), and its return value must
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be a POSTGRES base type (not necessarily the same
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as basetype.
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</para>
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</listitem>
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<listitem>
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<para>
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The final-calculation-function should be specified
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if and only if both state-transition functions are
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specified.
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</para
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</listitem>
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</itemizedlist>
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</PARA>
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<para>
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Note that it is possible to specify aggregate functions
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that have varying combinations of state and final functions.
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For example, the "count" aggregate requires sfunc2
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(an incrementing function) but not sfunc1 or finalfunc,
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whereas the "sum" aggregate requires sfunc1 (an addition
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function) but not sfunc2 or finalfunc and the "average"
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aggregate requires both of the above state functions as
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well as a finalfunc (a division function) to produce its
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answer. In any case, at least one state function must be
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defined, and any sfunc2 must have a corresponding initcond2.
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</para>
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<para>
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Aggregates also require two initial conditions, one for
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each transition function. These are specified and stored
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in the database as fields of type text.
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</para>
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<REFSECT2 ID="R2-SQL-CREATEAGGREGATE-3">
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<REFSECT2INFO>
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<DATE>1998-04-15</DATE>
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</REFSECT2INFO>
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<TITLE>
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Notes
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</TITLE>
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<PARA>
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CREATE AGGREGATE function is a PostgreSQL language extension.
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</PARA>
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<para>
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Refer to DROP AGGREGATE function to drop aggregate functions.
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</para>
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</REFSECT2>
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<REFSECT1 ID="R1-SQL-CREATEAGGREGATE-2">
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<TITLE>
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Usage
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</TITLE>
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<PARA>
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</PARA>
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<ProgramListing>
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</ProgramListing>
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</REFSECT1>
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<REFSECT1 ID="R1-SQL-CREATEAGGREGATE-3">
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<TITLE>
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Compatibility
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</TITLE>
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<PARA>
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</PARA>
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<REFSECT2 ID="R2-SQL-CREATEAGGREGATE-4">
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<REFSECT2INFO>
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<DATE>1998-04-15</DATE>
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</REFSECT2INFO>
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<TITLE>
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SQL92
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</TITLE>
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<PARA>
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There is no CREATE AGGREGATE function on SQL92.
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</PARA>
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</REFENTRY>
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<!-- Keep this comment at the end of the file
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Local variables:
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mode: sgml
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sgml-omittag:t
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sgml-shorttag:t
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sgml-minimize-attributes:nil
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sgml-always-quote-attributes:t
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sgml-indent-step:1
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sgml-indent-data:t
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sgml-parent-document:nil
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sgml-default-dtd-file:"../reference.ced"
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sgml-exposed-tags:nil
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sgml-local-catalogs:"/usr/lib/sgml/catalog"
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sgml-local-ecat-files:nil
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End:
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-->
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