Update aggregate-function docs for STDDEV, VARIANCE.
This commit is contained in:
Tom Lane
parent
bec98a31c5
commit
d06ebdb8d3
|
|
@ -1539,7 +1539,7 @@ Not defined by this name. Implements the intersection operator '#'
|
|||
|
||||
<para>
|
||||
<firstterm>Aggregate functions</firstterm> allow the generation of simple
|
||||
statistics about the values of particular columns over the selected set
|
||||
statistics about the values of given expressions over the selected set
|
||||
of rows.
|
||||
<!--
|
||||
See also <xref linkend="sql" endterm="aggregates-tutorial"> and
|
||||
|
|
@ -1556,6 +1556,7 @@ Not defined by this name. Implements the intersection operator '#'
|
|||
<title>Aggregate Functions</title>
|
||||
<tgroup cols="4">
|
||||
<thead>
|
||||
|
||||
<row>
|
||||
<entry>Function</entry>
|
||||
<entry>Returns</entry>
|
||||
|
|
@ -1563,6 +1564,7 @@ Not defined by this name. Implements the intersection operator '#'
|
|||
<entry>Example</entry>
|
||||
<entry>Notes</entry>
|
||||
</row>
|
||||
|
||||
</thead>
|
||||
<tbody>
|
||||
<row>
|
||||
|
|
@ -1572,45 +1574,85 @@ Not defined by this name. Implements the intersection operator '#'
|
|||
<entry>COUNT(*)</entry>
|
||||
<entry></entry>
|
||||
</row>
|
||||
|
||||
<row>
|
||||
<entry>COUNT(<replaceable class="parameter">column-name</replaceable>)</entry>
|
||||
<entry>COUNT(<replaceable class="parameter">expression</replaceable>)</entry>
|
||||
<entry>int4</entry>
|
||||
<entry>Counts the selected rows for which the value of <replaceable class="parameter">column-name</replaceable> is not NULL.</entry>
|
||||
<entry>Counts the selected rows for which the value of
|
||||
<replaceable class="parameter">expression</replaceable> is not
|
||||
NULL.</entry>
|
||||
<entry>COUNT(age)</entry>
|
||||
<entry></entry>
|
||||
</row>
|
||||
|
||||
<row>
|
||||
<entry>SUM(<replaceable class="parameter">column-name</replaceable>)</entry>
|
||||
<entry>Same as the data type of the column being summed.</entry>
|
||||
<entry>Finds the total obtained by adding the values of <replaceable class="parameter">column-name</replaceable> across all selected rows.</entry>
|
||||
<entry>SUM(<replaceable class="parameter">expression</replaceable>)</entry>
|
||||
<entry>Depends on the data type being summed.</entry>
|
||||
<entry>Finds the total obtained by adding the values of <replaceable class="parameter">expression</replaceable> across all selected rows.</entry>
|
||||
<entry>SUM(hours)</entry>
|
||||
<entry>Summation is supported on the following data types: int8, int4, int2, float4, float8, money, interval, numeric</entry>
|
||||
<entry>Summation is supported on the following data types: int8, int4,
|
||||
int2, float4, float8, money, interval, numeric. The result is numeric
|
||||
for any integer type, float8 for either float4 or float8 input,
|
||||
otherwise the same as the input data type.</entry>
|
||||
</row>
|
||||
|
||||
<row>
|
||||
<entry>MAX(<replaceable class="parameter">column-name</replaceable>)</entry>
|
||||
<entry>Same as the data type of the column whose maximum value is sought.</entry>
|
||||
<entry>The maximum value of <replaceable class="parameter">column-name</replaceable> across all selected rows.</entry>
|
||||
<entry>MAX(<replaceable class="parameter">expression</replaceable>)</entry>
|
||||
<entry>Same as the data type of the input expression.</entry>
|
||||
<entry>The maximum value of <replaceable class="parameter">expression</replaceable> across all selected rows.</entry>
|
||||
<entry>MAX(age)</entry>
|
||||
<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>
|
||||
</row>
|
||||
|
||||
<row>
|
||||
<entry>MIN(<replaceable class="parameter">column-name</replaceable>)</entry>
|
||||
<entry>same as the data type of the column whose minimum value is sought.</entry>
|
||||
<entry>The minimum value of <replaceable class="parameter">column-name</replaceable> across all selected rows.</entry>
|
||||
<entry>MIN(<replaceable class="parameter">expression</replaceable>)</entry>
|
||||
<entry>Same as the data type of the input expression.</entry>
|
||||
<entry>The minimum value of <replaceable class="parameter">expression</replaceable> across all selected rows.</entry>
|
||||
<entry>MIN(age)</entry>
|
||||
<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>
|
||||
</row>
|
||||
|
||||
<row>
|
||||
<entry>AVG(<replaceable class="parameter">column-name</replaceable>)</entry>
|
||||
<entry>Same as the data type of the column being averaged.</entry>
|
||||
<entry>The average (mean) of the values in the given column across all selected rows.</entry>
|
||||
<entry>AVG(age)</entry>
|
||||
<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>
|
||||
<entry>AVG(<replaceable class="parameter">expression</replaceable>)</entry>
|
||||
<entry>Depends on the data type being averaged.</entry>
|
||||
<entry>The average (mean) of the given values across all selected rows.</entry>
|
||||
<entry>AVG(age+1)</entry>
|
||||
<entry>Finding the mean value is supported on the following data
|
||||
types: int8, int4, int2, float4, float8, interval, numeric. The
|
||||
result is numeric for any integer type, float8 for either float4 or
|
||||
float8 input, otherwise the same as the input data type.</entry>
|
||||
</row>
|
||||
|
||||
<row>
|
||||
<entry>VARIANCE(<replaceable class="parameter">expression</replaceable>)</entry>
|
||||
<entry>Depends on the input data type.</entry>
|
||||
<entry>The sample variance of the given values.</entry>
|
||||
<entry>VARIANCE(reading)</entry>
|
||||
<entry>Finding the variance is supported on the following data
|
||||
types: int8, int4, int2, float4, float8, numeric. The result is
|
||||
float8 for float4 or float8 input, otherwise numeric.</entry>
|
||||
</row>
|
||||
|
||||
<row>
|
||||
<entry>STDDEV(<replaceable class="parameter">expression</replaceable>)</entry>
|
||||
<entry>Depends on the input data type.</entry>
|
||||
<entry>The sample standard deviation of the given values.</entry>
|
||||
<entry>STDDEV(reading)</entry>
|
||||
<entry>Finding the standard deviation is supported on the following
|
||||
data types: int8, int4, int2, float4, float8, numeric. The result is
|
||||
float8 for float4 or float8 input, otherwise numeric.</entry>
|
||||
</row>
|
||||
|
||||
</tbody>
|
||||
</tgroup>
|
||||
</table>
|
||||
</para>
|
||||
|
||||
<para>
|
||||
It should be noted that except for COUNT, these functions return NULL
|
||||
when no rows are selected. In particular, SUM of no rows returns NULL,
|
||||
not zero as one might expect.
|
||||
</para>
|
||||
</sect1>
|
||||
</chapter>
|
||||
|
||||
|
|
|
|||
Loading…
Reference in New Issue