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><DIV
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><H1
CLASS="SECT1"
><A
NAME="FUNCTIONS-AGGREGATE"
>6.14. Aggregate Functions</A
></H1
><P
> <I
CLASS="FIRSTTERM"
>Aggregate functions</I
> compute a single result
value from a set of input values. <A
HREF="functions-aggregate.html#FUNCTIONS-AGGREGATE-TABLE"
>Table 6-33</A
> show the built-in aggregate
functions. The special syntax considerations for aggregate
functions are explained in <A
HREF="sql-expressions.html#SYNTAX-AGGREGATES"
>Section 1.2.5</A
>.
Consult the <A
HREF="tutorial.html"
><I
>PostgreSQL 7.3.2 Tutorial</I
></A
> for additional introductory
information.
</P
><DIV
CLASS="TABLE"
><A
NAME="FUNCTIONS-AGGREGATE-TABLE"
></A
><P
><B
>Table 6-33. Aggregate Functions</B
></P
><TABLE
BORDER="1"
CLASS="CALSTABLE"
><THEAD
><TR
><TH
ALIGN="LEFT"
VALIGN="TOP"
>Function</TH
><TH
ALIGN="LEFT"
VALIGN="TOP"
>Argument Type</TH
><TH
ALIGN="LEFT"
VALIGN="TOP"
>Return Type</TH
><TH
ALIGN="LEFT"
VALIGN="TOP"
>Description</TH
><TD
> </TD
></TR
></THEAD
><TBODY
><TR
><TD
ALIGN="LEFT"
VALIGN="TOP"
> <A
NAME="AEN10355"
></A
>
<TT
CLASS="FUNCTION"
>avg(<TT
CLASS="REPLACEABLE"
><I
>expression</I
></TT
>)</TT
>
</TD
><TD
ALIGN="LEFT"
VALIGN="TOP"
> <TT
CLASS="TYPE"
>smallint</TT
>, <TT
CLASS="TYPE"
>integer</TT
>,
<TT
CLASS="TYPE"
>bigint</TT
>, <TT
CLASS="TYPE"
>real</TT
>, <TT
CLASS="TYPE"
>double
precision</TT
>, <TT
CLASS="TYPE"
>numeric</TT
>, or <TT
CLASS="TYPE"
>interval</TT
>.
</TD
><TD
ALIGN="LEFT"
VALIGN="TOP"
> <TT
CLASS="TYPE"
>numeric</TT
> for any integer type argument,
<TT
CLASS="TYPE"
>double precision</TT
> for a floating-point argument,
otherwise the same as the argument data type
</TD
><TD
ALIGN="LEFT"
VALIGN="TOP"
>the average (arithmetic mean) of all input values</TD
><TD
> </TD
></TR
><TR
><TD
ALIGN="LEFT"
VALIGN="TOP"
><TT
CLASS="FUNCTION"
>count(*)</TT
></TD
><TD
ALIGN="LEFT"
VALIGN="TOP"
> </TD
><TD
ALIGN="LEFT"
VALIGN="TOP"
><TT
CLASS="TYPE"
>bigint</TT
></TD
><TD
ALIGN="LEFT"
VALIGN="TOP"
>number of input values</TD
><TD
> </TD
></TR
><TR
><TD
ALIGN="LEFT"
VALIGN="TOP"
><TT
CLASS="FUNCTION"
>count(<TT
CLASS="REPLACEABLE"
><I
>expression</I
></TT
>)</TT
></TD
><TD
ALIGN="LEFT"
VALIGN="TOP"
>any</TD
><TD
ALIGN="LEFT"
VALIGN="TOP"
><TT
CLASS="TYPE"
>bigint</TT
></TD
><TD
ALIGN="LEFT"
VALIGN="TOP"
> number of input values for which the value of <TT
CLASS="REPLACEABLE"
><I
>expression</I
></TT
> is not null
</TD
><TD
> </TD
></TR
><TR
><TD
ALIGN="LEFT"
VALIGN="TOP"
><TT
CLASS="FUNCTION"
>max(<TT
CLASS="REPLACEABLE"
><I
>expression</I
></TT
>)</TT
></TD
><TD
ALIGN="LEFT"
VALIGN="TOP"
>any numeric, string, or date/time type</TD
><TD
ALIGN="LEFT"
VALIGN="TOP"
>same as argument type</TD
><TD
ALIGN="LEFT"
VALIGN="TOP"
> maximum value of <TT
CLASS="REPLACEABLE"
><I
>expression</I
></TT
> across all input
values
</TD
><TD
> </TD
></TR
><TR
><TD
ALIGN="LEFT"
VALIGN="TOP"
><TT
CLASS="FUNCTION"
>min(<TT
CLASS="REPLACEABLE"
><I
>expression</I
></TT
>)</TT
></TD
><TD
ALIGN="LEFT"
VALIGN="TOP"
>any numeric, string, or date/time type</TD
><TD
ALIGN="LEFT"
VALIGN="TOP"
>same as argument type</TD
><TD
ALIGN="LEFT"
VALIGN="TOP"
> minimum value of <TT
CLASS="REPLACEABLE"
><I
>expression</I
></TT
> across all input
values
</TD
><TD
> </TD
></TR
><TR
><TD
ALIGN="LEFT"
VALIGN="TOP"
> <A
NAME="AEN10406"
></A
>
<TT
CLASS="FUNCTION"
>stddev(<TT
CLASS="REPLACEABLE"
><I
>expression</I
></TT
>)</TT
>
</TD
><TD
ALIGN="LEFT"
VALIGN="TOP"
> <TT
CLASS="TYPE"
>smallint</TT
>, <TT
CLASS="TYPE"
>integer</TT
>,
<TT
CLASS="TYPE"
>bigint</TT
>, <TT
CLASS="TYPE"
>real</TT
>, <TT
CLASS="TYPE"
>double
precision</TT
>, or <TT
CLASS="TYPE"
>numeric</TT
>.
</TD
><TD
ALIGN="LEFT"
VALIGN="TOP"
> <TT
CLASS="TYPE"
>double precision</TT
> for floating-point arguments,
otherwise <TT
CLASS="TYPE"
>numeric</TT
>.
</TD
><TD
ALIGN="LEFT"
VALIGN="TOP"
>sample standard deviation of the input values</TD
><TD
> </TD
></TR
><TR
><TD
ALIGN="LEFT"
VALIGN="TOP"
><TT
CLASS="FUNCTION"
>sum(<TT
CLASS="REPLACEABLE"
><I
>expression</I
></TT
>)</TT
></TD
><TD
ALIGN="LEFT"
VALIGN="TOP"
> <TT
CLASS="TYPE"
>smallint</TT
>, <TT
CLASS="TYPE"
>integer</TT
>,
<TT
CLASS="TYPE"
>bigint</TT
>, <TT
CLASS="TYPE"
>real</TT
>, <TT
CLASS="TYPE"
>double
precision</TT
>, <TT
CLASS="TYPE"
>numeric</TT
>, or
<TT
CLASS="TYPE"
>interval</TT
>
</TD
><TD
ALIGN="LEFT"
VALIGN="TOP"
> <TT
CLASS="TYPE"
>bigint</TT
> for <TT
CLASS="TYPE"
>smallint</TT
> or
<TT
CLASS="TYPE"
>integer</TT
> arguments, <TT
CLASS="TYPE"
>numeric</TT
> for
<TT
CLASS="TYPE"
>bigint</TT
> arguments, <TT
CLASS="TYPE"
>double precision</TT
>
for floating-point arguments, otherwise the same as the
argument data type
</TD
><TD
ALIGN="LEFT"
VALIGN="TOP"
>sum of <TT
CLASS="REPLACEABLE"
><I
>expression</I
></TT
> across all input values</TD
><TD
> </TD
></TR
><TR
><TD
ALIGN="LEFT"
VALIGN="TOP"
> <A
NAME="AEN10444"
></A
>
<TT
CLASS="FUNCTION"
>variance</TT
>(<TT
CLASS="REPLACEABLE"
><I
>expression</I
></TT
>)
</TD
><TD
ALIGN="LEFT"
VALIGN="TOP"
> <TT
CLASS="TYPE"
>smallint</TT
>, <TT
CLASS="TYPE"
>integer</TT
>,
<TT
CLASS="TYPE"
>bigint</TT
>, <TT
CLASS="TYPE"
>real</TT
>, <TT
CLASS="TYPE"
>double
precision</TT
>, or <TT
CLASS="TYPE"
>numeric</TT
>.
</TD
><TD
ALIGN="LEFT"
VALIGN="TOP"
> <TT
CLASS="TYPE"
>double precision</TT
> for floating-point arguments,
otherwise <TT
CLASS="TYPE"
>numeric</TT
>.
</TD
><TD
ALIGN="LEFT"
VALIGN="TOP"
>sample variance of the input values (square of the sample standard deviation)</TD
><TD
> </TD
></TR
></TBODY
></TABLE
></DIV
><P
> It should be noted that except for <TT
CLASS="FUNCTION"
>count</TT
>,
these functions return a null value when no rows are selected. In
particular, <TT
CLASS="FUNCTION"
>sum</TT
> of no rows returns null, not
zero as one might expect. The function <TT
CLASS="FUNCTION"
>coalesce</TT
> may be
used to substitute zero for null when necessary.
</P
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