database/postgres
1
0
Fork 0
mirror of https://github.com/postgres/postgres.git synced 2025-12-21 05:21:08 +03:00
Code Activity

Update documentation to reflect availability of aggregate(DISTINCT).

Browse Source 
Try to provide a more lucid discussion in 'Using Aggregate Functions'
tutorial section.
This commit is contained in:
Tom Lane
1999-12-13 17:39:38 +00:00
parent 662371cc5d
commit ff6fe1502d
3 changed files with 111 additions and 36 deletions
Download Patch File Download Diff File Expand all files Collapse all files

21
doc/src/sgml/ref/select.sgml
View File

@@ -1,5 +1,5 @@
<!--
$Header: /cvsroot/pgsql/doc/src/sgml/ref/select.sgml,v 1.22 1999/08/06 13:50:31 thomas Exp $
$Header: /cvsroot/pgsql/doc/src/sgml/ref/select.sgml,v 1.23 1999/12/13 17:39:38 tgl Exp $
Postgres documentation
-->
@@ -202,10 +202,10 @@ SELECT [ ALL | DISTINCT [ ON <replaceable class="PARAMETER">column</replaceable>
<para>
<command>DISTINCT</command> will eliminate all duplicate rows from the
selection.
result.
<command>DISTINCT ON <replaceable class="PARAMETER">column</replaceable></command>
will eliminate all duplicates in the specified column; this is
equivalent to using
similar to using
<command>GROUP BY <replaceable class="PARAMETER">column</replaceable></command>.
<command>ALL</command> will return all candidate rows,
including duplicates.
@@ -320,11 +320,13 @@ GROUP BY <replaceable class="PARAMETER">column</replaceable> [, ...]
<para>
GROUP BY will condense into a single row all rows that share the
same values for the
grouped columns; aggregates return values derived from all rows
that make up the group. The value returned for an ungrouped
and unaggregated column is dependent on the order in which rows
happen to be read from the database.
same values for the grouped columns. Aggregate functions, if any,
are computed across all rows making up each group, producing a
separate value for each group (whereas without GROUP BY, an
aggregate produces a single value computed across all the selected
rows). When GROUP BY is present, it is not valid to refer to
ungrouped columns except within aggregate functions, since there
would be more than one possible value to return for an ungrouped column.
</para>
</refsect2>
@@ -354,7 +356,8 @@ HAVING <replaceable class="PARAMETER">cond_expr</replaceable>
<para>
Each column referenced in
<replaceable class="PARAMETER">cond_expr</replaceable> shall unambiguously
reference a grouping column.
reference a grouping column, unless the reference appears within an
aggregate function.
</para>
</refsect2>