Details
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Task
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Status: Closed (View Workflow)
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Major
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Resolution: Duplicate
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Description
The current sort based GROUP BY implementation performs badly when source data is large and expected output is small. An alternative method, supported by Oracle, Postgres, SQL Server, etc. is to use hash aggregation, as described here: http://blogs.msdn.com/b/craigfr/archive/2006/09/20/hash-aggregate.aspx