| From: | Lonni J Friedman <netllama(at)gmail(dot)com> |
|---|---|
| To: | Sam Z J <sammyjiang721(at)gmail(dot)com> |
| Cc: | pgsql-general(at)postgresql(dot)org |
| Subject: | Re: efficiency of wildcards at both ends |
| Date: | 2012-06-20 17:20:58 |
| Message-ID: | CAP=oouGs2wCLYxNT_hhG44u-2e40k6_iCmRtTn-x8sSXqvSxBA@mail.gmail.com |
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| Lists: | pgsql-general |
On Wed, Jun 20, 2012 at 10:10 AM, Sam Z J <sammyjiang721(at)gmail(dot)com> wrote:
> Hi all
>
> I'm curious how is wildcards at both ends implemented, e.g. LIKE '%str%'
> How efficient is it if that's the only search criteria against a large
> table? how much does indexing the column help and roughly how much more
> space is needed for the index?
>
> if the answers are too long, please point me to the relavant text =D
My limited understanding is that any time you need to resort to using
wildcards, indices are never used, and you're falling back to using
the inefficient table scan.
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