| From: | "Joshua D(dot) Drake" <jd(at)commandprompt(dot)com> |
|---|---|
| To: | "Robins Tharakan" <tharakan(at)gmail(dot)com> |
| Cc: | pgsql-performance(at)postgresql(dot)org |
| Subject: | Re: count * performance issue |
| Date: | 2008-03-11 03:08:44 |
| Message-ID: | 20080310200844.2281f0e8@jd-laptop |
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| Lists: | pgsql-performance |
On Tue, 11 Mar 2008 08:27:05 +0530
"Robins Tharakan" <tharakan(at)gmail(dot)com> wrote:
> SELECT COUNT(*) from table WHERE indexed_field IS NULL
> +
> SELECT COUNT(*) from table WHERE indexed_field IS NOT NULL
If the selectivity is appropriate yes. However if you have 1 million
rows, and 200k of those rows are null (or not null), it is still going
to seqscan.
joshua d. drake
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