From: | Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us> |
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To: | Heikki Linnakangas <heikki(dot)linnakangas(at)enterprisedb(dot)com> |
Cc: | Ian Barwick <barwick(at)gmail(dot)com>, pgsql-hackers <pgsql-hackers(at)postgresql(dot)org> |
Subject: | Re: 8.4b1: Query returning results in different order to 8.3 |
Date: | 2009-04-18 21:22:46 |
Message-ID: | 23286.1240089766@sss.pgh.pa.us |
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Heikki Linnakangas <heikki(dot)linnakangas(at)enterprisedb(dot)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...
regards, tom lane
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