| From: | Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us> |
|---|---|
| To: | "Nick Barr" <nick(dot)barr(at)webbased(dot)co(dot)uk> |
| Cc: | "'Patrick Welche'" <prlw1(at)newn(dot)cam(dot)ac(dot)uk>, csegyud(at)vnet(dot)hu, terry(at)ashtonwoodshomes(dot)com, "'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 15:15:41 |
| Message-ID: | 22128.1074179741@sss.pgh.pa.us |
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| Lists: | pgsql-general |
"Nick Barr" <nick(dot)barr(at)webbased(dot)co(dot)uk> writes:
>> Isn't there also a performance benefit as you can use an index if you
>> say "this definitely starts at the beginning" with the '^'?
> That is what I was thinking, which is the other reason why I put it in.
> This is only the case with the default locale I believe. I have no idea
> when it comes to regexs though and specifically the ~ operator. Could
> someone more knowledgeable about this stuff reply?
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 ^.
Locale and case sensitivity issues are the same, too.
regards, tom lane
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