| From: | Jean-Luc Lachance <jllachan(at)nsd(dot)ca> |
|---|---|
| To: | Neil Conway <nconway(at)klamath(dot)dyndns(dot)org> |
| Cc: | Doug Fields <dfields-pg-general(at)pexicom(dot)com>, pgsql-general(at)postgresql(dot)org |
| Subject: | Re: Spped of max |
| Date: | 2002-05-15 14:24:55 |
| Message-ID: | 3CE26FB7.97AB2704@nsd.ca |
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| Thread: | |
| Lists: | pgsql-general |
Neil Conway wrote:
>[...]
> If you don't have a qualification (i.e. SELECT count(*) FROM x), there
> are a couple ways to do it: use triggers to increment/decrement a
> counter of the number of rows in the table, create a btree-indexed
> SERIAL column and do an ORDER BY serial_column DESC LIMIT 1 on it (note
> that this is fragile, your sequence could easily have holes), or if you
> only need an approximation, you could use the pg_class attribute
> "reltuples" for the OID of your table. My impression is that most
> people choose the first method.
>
The real question is:
Why is reltuples only an approximation?
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