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Diffstat (limited to 'doc/src/sgml/ref/select.sgml')
| -rw-r--r-- | doc/src/sgml/ref/select.sgml | 23 |
1 files changed, 19 insertions, 4 deletions
diff --git a/doc/src/sgml/ref/select.sgml b/doc/src/sgml/ref/select.sgml index 15d9b75b59..916146df73 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 1.131 2010/06/15 20:04:53 momjian Exp $ +$PostgreSQL: pgsql/doc/src/sgml/ref/select.sgml,v 1.132 2010/08/07 02:44:05 tgl Exp $ PostgreSQL documentation --> @@ -520,9 +520,12 @@ GROUP BY <replaceable class="parameter">expression</replaceable> [, ...] produces a single value computed across all the selected rows). When <literal>GROUP BY</literal> is present, it is not valid for the <command>SELECT</command> list expressions to refer to - ungrouped columns except within aggregate functions, since there - would be more than one possible value to return for an ungrouped - column. + ungrouped columns except within aggregate functions or if the + ungrouped column is functionally dependent on the grouped columns, + since there would otherwise be more than one possible value to + return for an ungrouped column. A functional dependency exists if + the grouped columns (or a subset thereof) are the primary key of + the table containing the ungrouped column. </para> </refsect2> @@ -1591,6 +1594,18 @@ SELECT distributors.* WHERE distributors.name = 'Westward'; </refsect2> <refsect2> + <title>Functional Dependencies</title> + + <para> + <productname>PostgreSQL</productname> recognizes functional dependency + (allowing columns to be omitted from <literal>GROUP BY</>) only when + a table's primary key is included in the <literal>GROUP BY</> list. + The SQL standard specifies additional conditions that should be + recognized. + </para> + </refsect2> + + <refsect2> <title><literal>WINDOW</literal> Clause Restrictions</title> <para> |