| From: | Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us> |
|---|---|
| To: | Greg Stark <gsstark(at)mit(dot)edu> |
| Cc: | Joe Conway <mail(at)joeconway(dot)com>, pgsql-hackers(at)postgresql(dot)org |
| Subject: | Re: New array functions |
| Date: | 2003-08-28 23:04:19 |
| Message-ID: | 1090.1062111859@sss.pgh.pa.us |
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| Lists: | pgsql-hackers pgsql-patches |
Greg Stark <gsstark(at)mit(dot)edu> writes:
> Incidentally, "HashAggregate"?! Based on the earlier discussion on this I
> would have expected that line to read "Materialize"
It's using a grouped aggregation node to implement a UNIQUE filter, so
that it can replace the "WHERE foo IN (subselect)" by a straight join.
Of course in this case the uniqueness filter is a waste of time, but
in general the planner can't be expected to know that.
regards, tom lane
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