| From: | Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us> |
|---|---|
| To: | Nichlas Löfdahl <crotalus(at)acc(dot)umu(dot)se> |
| Cc: | pgsql-performance(at)postgresql(dot)org |
| Subject: | Re: Foreign keys and partial indexes |
| Date: | 2005-04-13 16:05:01 |
| Message-ID: | 7849.1113408301@sss.pgh.pa.us |
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| Lists: | pgsql-performance |
Nichlas =?iso-8859-1?Q?L=F6fdahl?= <crotalus(at)acc(dot)umu(dot)se> writes:
> I have a partial index (btree(col) WHERE col > 0) on table2 ('col' contains alot of NULL-values).
> There's also a foreign key on the column pointing to the primary key of table1 (ON UPDATE CASCADE ON DELETE SET NULL). During update/delete, it seems like it cannot use the partial index to find corresponding rows matching the foreign key (doing a full seqscan instead)?
> Is there any special reason for not letting the planner use the partial index when appropriate?
It doesn't know it's appropriate. There's nothing constraining the FK
to be positive, after all.
regards, tom lane
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