Re: efficiency of wildcards at both ends

thank you all for the useful information =D

On Wed, Jun 20, 2012 at 1:39 PM, Alan Hodgson <ahodgson(at)simkin(dot)ca> wrote:

> On Wednesday, June 20, 2012 01:10:03 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?
> >
>
> Indexing helps not at all. If the search string starts with a wildcard you
> will always get a sequential scan of the whole table.
>
> Look at the full text search documentation for a better approach.
>
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--
Zhongshi (Sam) Jiang
sammyjiang721(at)gmail(dot)com