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Update aggregate-function docs for STDDEV, VARIANCE.
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‎doc/src/sgml/func.sgml

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@@ -1539,7 +1539,7 @@ Not defined by this name. Implements the intersection operator '#'
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<para>
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<firstterm>Aggregate functions</firstterm> allow the generation of simple
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statistics about the values of particular columns over the selected set
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statistics about the values of given expressions over the selected set
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of rows.
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<!--
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See also <xref linkend="sql" endterm="aggregates-tutorial"> and
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<title>Aggregate Functions</title>
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<tgroup cols="4">
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<thead>
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<row>
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<entry>Function</entry>
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<entry>Returns</entry>
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<entry>Description</entry>
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<entry>Example</entry>
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<entry>Notes</entry>
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</row>
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</thead>
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<tbody>
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<row>
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<entry>COUNT(*)</entry>
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<entry></entry>
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</row>
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<row>
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<entry>COUNT(<replaceable class="parameter">column-name</replaceable>)</entry>
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<entry>COUNT(<replaceable class="parameter">expression</replaceable>)</entry>
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<entry>int4</entry>
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<entry>Counts the selected rows for which the value of <replaceable class="parameter">column-name</replaceable> is not NULL.</entry>
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<entry>Counts the selected rows for which the value of
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<replaceable class="parameter">expression</replaceable> is not
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NULL.</entry>
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<entry>COUNT(age)</entry>
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<entry></entry>
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</row>
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<row>
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<entry>SUM(<replaceable class="parameter">column-name</replaceable>)</entry>
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<entry>Same as the data type of the column being summed.</entry>
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<entry>Finds the total obtained by adding the values of <replaceable class="parameter">column-name</replaceable> across all selected rows.</entry>
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<entry>SUM(<replaceable class="parameter">expression</replaceable>)</entry>
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<entry>Depends on the data type being summed.</entry>
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<entry>Finds the total obtained by adding the values of <replaceable class="parameter">expression</replaceable> across all selected rows.</entry>
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<entry>SUM(hours)</entry>
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<entry>Summation is supported on the following data types: int8, int4, int2, float4, float8, money, interval, numeric</entry>
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<entry>Summation is supported on the following data types: int8, int4,
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int2, float4, float8, money, interval, numeric. The result is numeric
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for any integer type, float8 for either float4 or float8 input,
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otherwise the same as the input data type.</entry>
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</row>
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<row>
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<entry>MAX(<replaceable class="parameter">column-name</replaceable>)</entry>
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<entry>Same as the data type of the column whose maximum value is sought.</entry>
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<entry>The maximum value of <replaceable class="parameter">column-name</replaceable> across all selected rows.</entry>
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<entry>MAX(<replaceable class="parameter">expression</replaceable>)</entry>
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<entry>Same as the data type of the input expression.</entry>
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<entry>The maximum value of <replaceable class="parameter">expression</replaceable> across all selected rows.</entry>
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<entry>MAX(age)</entry>
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<entry>Finding the maximum value is supported on the following data types: int8, int4, int2, float4, float8, date, time, timetz, money, timestamp, interval, text, numeric.</entry>
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</row>
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<row>
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<entry>MIN(<replaceable class="parameter">column-name</replaceable>)</entry>
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<entry>same as the data type of the column whose minimum value is sought.</entry>
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<entry>The minimum value of <replaceable class="parameter">column-name</replaceable> across all selected rows.</entry>
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<entry>MIN(<replaceable class="parameter">expression</replaceable>)</entry>
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<entry>Same as the data type of the input expression.</entry>
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<entry>The minimum value of <replaceable class="parameter">expression</replaceable> across all selected rows.</entry>
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<entry>MIN(age)</entry>
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<entry>Finding the minimum value is supported on the following data types: int8, int4, int2, float4, float8, date, time, timetz, money, timestamp, interval, text, numeric.</entry>
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</row>
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<row>
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<entry>AVG(<replaceable class="parameter">column-name</replaceable>)</entry>
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<entry>Same as the data type of the column being averaged.</entry>
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<entry>The average (mean) of the values in the given column across all selected rows.</entry>
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<entry>AVG(age)</entry>
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<entry>Finding the mean value is supported on the following data types: int8, int4, int2, float4, float8, money, interval, numeric. Note that as the return type is the same as that of the data being averaged, using AVG() on discrete data will give a rounded result.</entry>
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<entry>AVG(<replaceable class="parameter">expression</replaceable>)</entry>
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<entry>Depends on the data type being averaged.</entry>
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<entry>The average (mean) of the given values across all selected rows.</entry>
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<entry>AVG(age+1)</entry>
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<entry>Finding the mean value is supported on the following data
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types: int8, int4, int2, float4, float8, interval, numeric. The
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result is numeric for any integer type, float8 for either float4 or
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float8 input, otherwise the same as the input data type.</entry>
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</row>
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<row>
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<entry>VARIANCE(<replaceable class="parameter">expression</replaceable>)</entry>
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<entry>Depends on the input data type.</entry>
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<entry>The sample variance of the given values.</entry>
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<entry>VARIANCE(reading)</entry>
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<entry>Finding the variance is supported on the following data
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types: int8, int4, int2, float4, float8, numeric. The result is
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float8 for float4 or float8 input, otherwise numeric.</entry>
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</row>
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<row>
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<entry>STDDEV(<replaceable class="parameter">expression</replaceable>)</entry>
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<entry>Depends on the input data type.</entry>
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<entry>The sample standard deviation of the given values.</entry>
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<entry>STDDEV(reading)</entry>
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<entry>Finding the standard deviation is supported on the following
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data types: int8, int4, int2, float4, float8, numeric. The result is
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float8 for float4 or float8 input, otherwise numeric.</entry>
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</row>
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</tbody>
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</tgroup>
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</table>
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</para>
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<para>
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It should be noted that except for COUNT, these functions return NULL
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when no rows are selected. In particular, SUM of no rows returns NULL,
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not zero as one might expect.
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</para>
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</sect1>
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</chapter>
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