From: | Andy Colson <andy(at)squeakycode(dot)net> |
---|---|
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 17:22:41 |
Message-ID: | 4FE206E1.6010702@squeakycode.net |
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Thread: | |
Lists: | pgsql-general |
On 6/20/2012 12:10 PM, Sam Z J 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
>
> thanks
>
> --
> Zhongshi (Sam) Jiang
> sammyjiang721(at)gmail(dot)com <mailto:sammyjiang721(at)gmail(dot)com>
An index will not be used for that kind of search. PG will scan the
entire table to find matches. PG can only use an index if you have a
search LIKE 'str%'
There are options like full text search, and pg_trgm that you might be
able to use.
-Andy
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