| From: | Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us> |
|---|---|
| To: | Karsten Hilbert <Karsten(dot)Hilbert(at)gmx(dot)net> |
| Cc: | "'Pgsql-General(at)Postgresql(dot)Org (E-mail)'" <pgsql-general(at)postgresql(dot)org> |
| Subject: | Re: Using regular expressions in LIKE |
| Date: | 2004-01-15 16:28:11 |
| Message-ID: | 22683.1074184091@sss.pgh.pa.us |
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| Lists: | pgsql-general |
Karsten Hilbert <Karsten(dot)Hilbert(at)gmx(dot)net> writes:
>> Regexes are optimized the same way as equivalent LIKE expressions. In
>> particular, the pattern has to be left-anchored to consider using it
>> with an index. In LIKE that means no wildcard at the start of the
>> pattern, in regex it means there has to be a ^.
> What about "^.*oobar" in a regex ? I mean, it seems impossible
> to use an index on that, right ?
Right. You need ^ immediately followed by some constant text. The
planner extracts the "fixed prefix" of the pattern to use with the index.
regards, tom lane
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