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Diffstat (limited to 'doc/src/sgml/ref/update.sgml')
| -rw-r--r-- | doc/src/sgml/ref/update.sgml | 22 |
1 files changed, 21 insertions, 1 deletions
diff --git a/doc/src/sgml/ref/update.sgml b/doc/src/sgml/ref/update.sgml index 48d160b2ec..3fc3144dfe 100644 --- a/doc/src/sgml/ref/update.sgml +++ b/doc/src/sgml/ref/update.sgml @@ -1,5 +1,5 @@ <!-- -$PostgreSQL: pgsql/doc/src/sgml/ref/update.sgml,v 1.30 2004/08/08 01:48:31 momjian Exp $ +$PostgreSQL: pgsql/doc/src/sgml/ref/update.sgml,v 1.31 2005/01/04 03:58:16 tgl Exp $ PostgreSQL documentation --> @@ -151,6 +151,26 @@ UPDATE <replaceable class="parameter">count</replaceable> </refsect1> <refsect1> + <title>Notes</title> + + <para> + When joining the target table to other tables using a <replaceable + class="PARAMETER">fromlist</replaceable>, be careful that the join + produces at most one output row for each row to be modified. In + other words, a target row mustn't join to more than one row from + the other table(s). If it does, then only one of the join rows + will be used to update the target row, but which one will be used + is not readily predictable. + </para> + + <para> + Because of this indeterminancy, referencing other tables only within + sub-selects is safer, though often harder to read and slower than + using a join. + </para> + </refsect1> + + <refsect1> <title>Examples</title> <para> |