diff options
Diffstat (limited to 'doc/src')
| -rw-r--r-- | doc/src/sgml/query.sgml | 7 | ||||
| -rw-r--r-- | doc/src/sgml/ref/select.sgml | 13 |
2 files changed, 16 insertions, 4 deletions
diff --git a/doc/src/sgml/query.sgml b/doc/src/sgml/query.sgml index 366820e5546..e573db56cb6 100644 --- a/doc/src/sgml/query.sgml +++ b/doc/src/sgml/query.sgml @@ -1,5 +1,5 @@ <!-- -$PostgreSQL: pgsql/doc/src/sgml/query.sgml,v 1.43 2005/01/22 22:56:36 momjian Exp $ +$PostgreSQL: pgsql/doc/src/sgml/query.sgml,v 1.44 2005/03/10 23:21:20 tgl Exp $ --> <chapter id="tutorial-sql"> @@ -783,8 +783,9 @@ SELECT city, max(temp_lo) will be inputs to the aggregates. On the other hand, the <literal>HAVING</literal> clause always contains aggregate functions. (Strictly speaking, you are allowed to write a <literal>HAVING</literal> - clause that doesn't use aggregates, but it's wasteful. The same condition - could be used more efficiently at the <literal>WHERE</literal> stage.) + clause that doesn't use aggregates, but it's seldom useful. The same + condition could be used more efficiently at the <literal>WHERE</literal> + stage.) </para> <para> diff --git a/doc/src/sgml/ref/select.sgml b/doc/src/sgml/ref/select.sgml index 855412c36c9..93218e16c2e 100644 --- a/doc/src/sgml/ref/select.sgml +++ b/doc/src/sgml/ref/select.sgml @@ -1,5 +1,5 @@ <!-- -$PostgreSQL: pgsql/doc/src/sgml/ref/select.sgml,v 1.81 2005/01/22 23:22:19 momjian Exp $ +$PostgreSQL: pgsql/doc/src/sgml/ref/select.sgml,v 1.82 2005/03/10 23:21:20 tgl Exp $ PostgreSQL documentation --> @@ -452,6 +452,17 @@ HAVING <replaceable class="parameter">condition</replaceable> unambiguously reference a grouping column, unless the reference appears within an aggregate function. </para> + + <para> + The presence of <literal>HAVING</literal> turns a query into a grouped + query even if there is no <literal>GROUP BY</> clause. This is the + same as what happens when the query contains aggregate functions but + no <literal>GROUP BY</> clause. All the selected rows are considered to + form a single group, and the <command>SELECT</command> list and + <literal>HAVING</literal> clause can only reference table columns from + within aggregate functions. Such a query will emit a single row if the + <literal>HAVING</literal> condition is true, zero rows if it is not true. + </para> </refsect2> <refsect2 id="sql-select-list"> |