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Message Posted: Thu, 27 Mar 2008 @ 20:42:52 GMT

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Subj:   Re: How GROUP BY improves the performance than
From:   Anomy Anom

<-- Anonymously Posted: Thu, 27 Mar 2008 13:00 -->

Conceptually, DISTINCT builds the entire answer set, then removes duplicates. GROUP BY may be able to do the aggregation sooner and/or do "AMP- local" partial aggregation - but there is extra overhead, so if very few rows are eliminated the DISTINCT actually performs better.

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