Re: 8.4b1: Query returning results in different order to 8.3

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. You can look at the EXPLAIN output to 
see the difference.

--   Heikki Linnakangas  EnterpriseDB   http://www.enterprisedb.com