--- Tom Lane wrote: >
=?iso-8859-1?q?Gary=20Cowell?=
<gary_cowell@yahoo.co.uk> writes:
So it seems the idea that oracle is dropping duplicate
rows prior to the sort when using distinct may indeed
be the case.
Okay. We won't have any short-term solution for
making DISTINCT do that,
but if you are on PG 7.4 you could get the same
effect from using
GROUP BY: instead of
select distinct version from vers where version is
not null
try
select version from vers where version is not null
group by version
You should get a HashAggregate plan out of that, and
I'd think it'd be
pretty quick when there are not many distinct values
of version.
Yeah out of the half million rows there are only ever
going to be 500 or so distinct values.

I do indeed get such a plan. It's much faster that
way. Down to 16 seconds. I'll get the chap to rewrite
his app to use group by instead of distinct.

Thanks (everyone) for the top class help!





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postedJun 18, '04 at 11:32a
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