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><DIV
CLASS="SECT1"
><H1
CLASS="SECT1"
><A
NAME="FUNCTIONS-AGGREGATE"
>9.15. Aggregate Functions</A
></H1
><A
NAME="AEN12936"
></A
><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 9-37</A
> shows the built-in aggregate
   functions.  The special syntax considerations for aggregate
   functions are explained in <A
HREF="sql-expressions.html#SYNTAX-AGGREGATES"
>Section 4.2.7</A
>.
   Consult <A
HREF="tutorial-agg.html"
>Section 2.7</A
> for additional introductory
   information.
  </P
><DIV
CLASS="TABLE"
><A
NAME="FUNCTIONS-AGGREGATE-TABLE"
></A
><P
><B
>Table 9-37. Aggregate Functions</B
></P
><TABLE
BORDER="1"
CLASS="CALSTABLE"
><COL><COL><COL><COL><THEAD
><TR
><TH
>Function</TH
><TH
>Argument Type</TH
><TH
>Return Type</TH
><TH
>Description</TH
></TR
></THEAD
><TBODY
><TR
><TD
>       <A
NAME="AEN12956"
></A
>
       <CODE
CLASS="FUNCTION"
>avg(<TT
CLASS="REPLACEABLE"
><I
>expression</I
></TT
>)</CODE
>
      </TD
><TD
>       <TT
CLASS="TYPE"
>smallint</TT
>, <TT
CLASS="TYPE"
>int</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
>       <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
>the average (arithmetic mean) of all input values</TD
></TR
><TR
><TD
>       <A
NAME="AEN12974"
></A
>
       <CODE
CLASS="FUNCTION"
>bit_and(<TT
CLASS="REPLACEABLE"
><I
>expression</I
></TT
>)</CODE
>
      </TD
><TD
>       <TT
CLASS="TYPE"
>smallint</TT
>, <TT
CLASS="TYPE"
>int</TT
>, <TT
CLASS="TYPE"
>bigint</TT
>, or
       <TT
CLASS="TYPE"
>bit</TT
>
      </TD
><TD
>        same as argument data type
      </TD
><TD
>the bitwise AND of all non-null input values, or null if none</TD
></TR
><TR
><TD
>       <A
NAME="AEN12987"
></A
>
       <CODE
CLASS="FUNCTION"
>bit_or(<TT
CLASS="REPLACEABLE"
><I
>expression</I
></TT
>)</CODE
>
      </TD
><TD
>       <TT
CLASS="TYPE"
>smallint</TT
>, <TT
CLASS="TYPE"
>int</TT
>, <TT
CLASS="TYPE"
>bigint</TT
>, or
       <TT
CLASS="TYPE"
>bit</TT
>
      </TD
><TD
>        same as argument data type
      </TD
><TD
>the bitwise OR of all non-null input values, or null if none</TD
></TR
><TR
><TD
>       <A
NAME="AEN13000"
></A
>
       <CODE
CLASS="FUNCTION"
>bool_and(<TT
CLASS="REPLACEABLE"
><I
>expression</I
></TT
>)</CODE
>
      </TD
><TD
>       <TT
CLASS="TYPE"
>bool</TT
>
      </TD
><TD
>       <TT
CLASS="TYPE"
>bool</TT
>
      </TD
><TD
>true if all input values are true, otherwise false</TD
></TR
><TR
><TD
>       <A
NAME="AEN13011"
></A
>
       <CODE
CLASS="FUNCTION"
>bool_or(<TT
CLASS="REPLACEABLE"
><I
>expression</I
></TT
>)</CODE
>
      </TD
><TD
>       <TT
CLASS="TYPE"
>bool</TT
>
      </TD
><TD
>       <TT
CLASS="TYPE"
>bool</TT
>
      </TD
><TD
>true if at least one input value is true, otherwise false</TD
></TR
><TR
><TD
><CODE
CLASS="FUNCTION"
>count(*)</CODE
></TD
><TD
>&nbsp;</TD
><TD
><TT
CLASS="TYPE"
>bigint</TT
></TD
><TD
>number of input values</TD
></TR
><TR
><TD
><CODE
CLASS="FUNCTION"
>count(<TT
CLASS="REPLACEABLE"
><I
>expression</I
></TT
>)</CODE
></TD
><TD
>any</TD
><TD
><TT
CLASS="TYPE"
>bigint</TT
></TD
><TD
>       number of input values for which the value of <TT
CLASS="REPLACEABLE"
><I
>expression</I
></TT
> is not null
      </TD
></TR
><TR
><TD
>       <A
NAME="AEN13038"
></A
>
       <CODE
CLASS="FUNCTION"
>every(<TT
CLASS="REPLACEABLE"
><I
>expression</I
></TT
>)</CODE
>
      </TD
><TD
>       <TT
CLASS="TYPE"
>bool</TT
>
      </TD
><TD
>       <TT
CLASS="TYPE"
>bool</TT
>
      </TD
><TD
>equivalent to <CODE
CLASS="FUNCTION"
>bool_and</CODE
></TD
></TR
><TR
><TD
><CODE
CLASS="FUNCTION"
>max(<TT
CLASS="REPLACEABLE"
><I
>expression</I
></TT
>)</CODE
></TD
><TD
>any array, numeric, string, or date/time type</TD
><TD
>same as argument type</TD
><TD
>       maximum value of <TT
CLASS="REPLACEABLE"
><I
>expression</I
></TT
> across all input
       values
      </TD
></TR
><TR
><TD
><CODE
CLASS="FUNCTION"
>min(<TT
CLASS="REPLACEABLE"
><I
>expression</I
></TT
>)</CODE
></TD
><TD
>any array, numeric, string, or date/time type</TD
><TD
>same as argument type</TD
><TD
>       minimum value of <TT
CLASS="REPLACEABLE"
><I
>expression</I
></TT
> across all input
       values
      </TD
></TR
><TR
><TD
>       <A
NAME="AEN13066"
></A
>
       <CODE
CLASS="FUNCTION"
>stddev(<TT
CLASS="REPLACEABLE"
><I
>expression</I
></TT
>)</CODE
>
      </TD
><TD
>       <TT
CLASS="TYPE"
>smallint</TT
>, <TT
CLASS="TYPE"
>int</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
>       <TT
CLASS="TYPE"
>double precision</TT
> for floating-point arguments,
       otherwise <TT
CLASS="TYPE"
>numeric</TT
>
      </TD
><TD
>sample standard deviation of the input values</TD
></TR
><TR
><TD
><CODE
CLASS="FUNCTION"
>sum(<TT
CLASS="REPLACEABLE"
><I
>expression</I
></TT
>)</CODE
></TD
><TD
>       <TT
CLASS="TYPE"
>smallint</TT
>, <TT
CLASS="TYPE"
>int</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
>       <TT
CLASS="TYPE"
>bigint</TT
> for <TT
CLASS="TYPE"
>smallint</TT
> or
       <TT
CLASS="TYPE"
>int</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
>sum of <TT
CLASS="REPLACEABLE"
><I
>expression</I
></TT
> across all input values</TD
></TR
><TR
><TD
>       <A
NAME="AEN13104"
></A
>
       <CODE
CLASS="FUNCTION"
>variance</CODE
>(<TT
CLASS="REPLACEABLE"
><I
>expression</I
></TT
>)
      </TD
><TD
>       <TT
CLASS="TYPE"
>smallint</TT
>, <TT
CLASS="TYPE"
>int</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
>       <TT
CLASS="TYPE"
>double precision</TT
> for floating-point arguments,
       otherwise <TT
CLASS="TYPE"
>numeric</TT
>
      </TD
><TD
>sample variance of the input values (square of the sample standard deviation)</TD
></TR
></TBODY
></TABLE
></DIV
><P
>   It should be noted that except for <CODE
CLASS="FUNCTION"
>count</CODE
>,
   these functions return a null value when no rows are selected.  In
   particular, <CODE
CLASS="FUNCTION"
>sum</CODE
> of no rows returns null, not
   zero as one might expect.  The <CODE
CLASS="FUNCTION"
>coalesce</CODE
> function may be
   used to substitute zero for null when necessary.
  </P
><DIV
CLASS="NOTE"
><BLOCKQUOTE
CLASS="NOTE"
><A
NAME="AEN13124"
></A
><A
NAME="AEN13126"
></A
><P
><B
>Note: </B
>      Boolean aggregates <CODE
CLASS="FUNCTION"
>bool_and</CODE
> and 
      <CODE
CLASS="FUNCTION"
>bool_or</CODE
> correspond to standard SQL aggregates
      <CODE
CLASS="FUNCTION"
>every</CODE
> and <CODE
CLASS="FUNCTION"
>any</CODE
> or
      <CODE
CLASS="FUNCTION"
>some</CODE
>. 
      As for <CODE
CLASS="FUNCTION"
>any</CODE
> and <CODE
CLASS="FUNCTION"
>some</CODE
>, 
      it seems that there is an ambiguity built into the standard syntax:
</P><PRE
CLASS="PROGRAMLISTING"
>SELECT b1 = ANY((SELECT b2 FROM t2 ...)) FROM t1 ...;</PRE
><P>
      Here <CODE
CLASS="FUNCTION"
>ANY</CODE
> can be considered both as leading
      to a subquery or as an aggregate if the select expression returns 1 row.
      Thus the standard name cannot be given to these aggregates.
    </P
></BLOCKQUOTE
></DIV
><DIV
CLASS="NOTE"
><BLOCKQUOTE
CLASS="NOTE"
><P
><B
>Note: </B
>    Users accustomed to working with other SQL database management
    systems may be surprised by the performance of the
    <CODE
CLASS="FUNCTION"
>count</CODE
> aggregate when it is applied to the
    entire table. A query like:
</P><PRE
CLASS="PROGRAMLISTING"
>SELECT count(*) FROM sometable;</PRE
><P>
    will be executed by <SPAN
CLASS="PRODUCTNAME"
>PostgreSQL</SPAN
> using a
    sequential scan of the entire table.
   </P
></BLOCKQUOTE
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