| From: | Josh Berkus <josh(at)agliodbs(dot)com> |
|---|---|
| To: | Reece Hart <reece(at)harts(dot)net> |
| Cc: | SF PostgreSQL <sfpug(at)postgresql(dot)org> |
| Subject: | Re: query plans and immutable functions |
| Date: | 2006-05-10 00:16:07 |
| Message-ID: | 446130C7.9090603@agliodbs.com |
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| Lists: | sfpug |
Reece,
> When md5() is explicitly cast to bpchar, the index is used. I ran
> across this issue long ago (in 7.x), but I thought that casting was now
> part of query optimization and that explicit casting was no longer
> required. I was wrong.
Well, the planner tries to figure out the casting. Sometimes it fails.
CHAR is particularly problematic in this regard; it's not exactly
equivalent to TEXT so the plannner can fail to match it up.
Your solution of course, is to create a shell function for md5 which
converts it to CHAR. Or just cast.
--Josh Berkus
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