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Re: Partial match in GIN

From: Alvaro Herrera <alvherre(at)commandprompt(dot)com>
To: Heikki Linnakangas <heikki(at)enterprisedb(dot)com>
Cc: Teodor Sigaev <teodor(at)sigaev(dot)ru>, Patches <pgsql-patches(at)postgresql(dot)org>
Subject: Re: Partial match in GIN
Date: 2008-04-08 19:49:00
Message-ID: 20080408194900.GQ9062@alvh.no-ip.org (view raw or flat)
Thread:
Lists: pgsql-patches
Heikki Linnakangas wrote:
> Alvaro Herrera wrote:
>> Heikki Linnakangas wrote:

>>> You could satisfy '%foo%' using a regular and a reverse B-tree index, 
>>>  and a bitmap AND. Which is interestingly similar to the way you 
>>> proposed  to use a TIDBitmap within GIN.
>>
>> Huh, can you?  I can see doing "col LIKE 'foo%' OR reverse(col) LIKE
>> reverse('%foo')" with two btree indexes, but not a true %foo% ...
>
> That should be AND, not OR..
>
> Hmm. It is the same as far as I can see. Am I missing something?

Well, LIKE %foo% is supposed to match foo unanchored, but with a btree
(or two btrees) you can only get 'foo' anchored to either end of the
string (or both).

-- 
Alvaro Herrera                                http://www.CommandPrompt.com/
The PostgreSQL Company - Command Prompt, Inc.

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