From d06ebdb8d3425185d7e641d15e45908658a0177d Mon Sep 17 00:00:00 2001
From: Tom Lane <tgl@sss.pgh.pa.us>
Date: Mon, 17 Jul 2000 03:52:28 +0000
Subject: [PATCH] Update aggregate-function docs for STDDEV, VARIANCE.
---
doc/src/sgml/func.sgml | 78 ++++++++++++++++++++++++++++++++----------
1 file changed, 60 insertions(+), 18 deletions(-)
diff --git a/doc/src/sgml/func.sgml b/doc/src/sgml/func.sgml
index 1e393c623bc..09524f8518d 100644
--- a/doc/src/sgml/func.sgml
+++ b/doc/src/sgml/func.sgml
@@ -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>
--
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