| From: | Ben <bench(at)silentmedia(dot)com> |
|---|---|
| To: | Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us> |
| Cc: | Simon Riggs <simon(at)2ndquadrant(dot)com>, pgsql-performance(at)postgresql(dot)org |
| Subject: | Re: quickly getting the top N rows |
| Date: | 2007-10-04 21:16:49 |
| Message-ID: | Pine.LNX.4.64.0710041414590.30864@localhost.localdomain |
| Views: | Raw Message | Whole Thread | Download mbox | Resend email |
| Thread: | |
| Lists: | pgsql-performance |
On Thu, 4 Oct 2007, Tom Lane wrote:
> There's some limited smarts in there about deciding that leading columns
> of an index don't matter to the sort ordering if they're constrained to
> just one value by the query. But it doesn't catch the case you need,
> which is that columns of an ORDER BY request are no-ops when they're
> constrained to just one value.
Oh, no, that explains it perfectly, because that's precisely the case I
have - I dropped the columns from the ordering, but not the where clause.
Thanks, now I understand the current behavior.
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