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Merge documentation updates from 7.3 branch.

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Peter Eisentraut
2002-11-11 20:14:04 +00:00
parent b327906683
commit 1b342df00a
28 changed files with 2330 additions and 2479 deletions
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doc/src/sgml/queries.sgml
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@@ -1,4 +1,4 @@
<!-- $Header: /cvsroot/pgsql/doc/src/sgml/queries.sgml,v 1.18 2002/10/20 05:05:46 tgl Exp $ -->
<!-- $Header: /cvsroot/pgsql/doc/src/sgml/queries.sgml,v 1.19 2002/11/11 20:14:03 petere Exp $ -->
<chapter id="queries">
<title>Queries</title>
@@ -668,7 +668,7 @@ SELECT <replaceable>select_list</replaceable>
order in which the columns are listed does not matter. The
purpose is to reduce each group of rows sharing common values into
one group row that is representative of all rows in the group.
This is done to eliminate redundancy in the output and/or obtain
This is done to eliminate redundancy in the output and/or compute
aggregates that apply to these groups. For instance:
<screen>
<prompt>=></> <userinput>SELECT * FROM test1;</>
@@ -694,7 +694,12 @@ SELECT <replaceable>select_list</replaceable>
In the second query, we could not have written <literal>SELECT *
FROM test1 GROUP BY x</literal>, because there is no single value
for the column <literal>y</> that could be associated with each
group. In general, if a table is grouped, columns that are not
group. The grouped-by columns can be referenced in the select list since
they have a known constant value per group.
</para>
<para>
In general, if a table is grouped, columns that are not
used in the grouping cannot be referenced except in aggregate
expressions. An example with aggregate expressions is:
<screen>
@@ -712,11 +717,6 @@ SELECT <replaceable>select_list</replaceable>
linkend="functions-aggregate">.
</para>
<para>
The grouped-by columns can be referenced in the select list since
they have a known constant value per group.
</para>
<tip>
<para>
Grouping without aggregate expressions effectively calculates the
@@ -740,7 +740,7 @@ SELECT product_id, p.name, (sum(s.units) * p.price) AS sales
in the <literal>GROUP BY</> clause since they are referenced in
the query select list. (Depending on how exactly the products
table is set up, name and price may be fully dependent on the
product ID, so the additional groups could theoretically be
product ID, so the additional groupings could theoretically be
unnecessary, but this is not implemented yet.) The column
<literal>s.units</> does not have to be in the <literal>GROUP
BY</> list since it is only used in an aggregate expression
@@ -828,7 +828,7 @@ SELECT product_id, p.name, (sum(s.units) * (p.price - p.cost)) AS profit
</para>
<sect2 id="queries-select-list-items">
<title>Select List Items</title>
<title>Select-List Items</title>
<para>
The simplest kind of select list is <literal>*</literal> which