2009/4/19 Tom Lane <t...@sss.pgh.pa.us> > Heikki Linnakangas <heikki.linnakan...@enterprisedb.com> writes: > > Ian Barwick wrote: > >> Note I'm not sure whether this is a bug, or whether the assumption > >> made for the original query (that the row order returned by the > >> subquery would be carried over to the main part of the query) is > >> incorrect but just happened to work as expected pre-8.4. > > > The latter. Without an ORDER BY (at the outermost level), the order of > > the result is not well defined. Before 8.4, UNION was always performed > > by a Sort + Unique, which explains why the output is always sorted in > > previous releases. 8.4 knows how to perform it with a Hash Aggregate, > > which doesn't yield sorted output. > > This is mentioned in the release notes, but I suppose we'd better > promote it to the "observe the following incompatibilities" list... >
Thanks for clarifying that. The relevant section in the release notes (which I managed to miss) is this: http://www.postgresql.org/docs/8.4/static/release-8-4.html#AEN93685 It would certainly be worth an explicit mention as I imagine the previous behaviour has been consistent enough for queries to have come to rely on it. Regards Ian Barwick
