Re: How to get around LIKE inefficiencies?

At 21:28 5/11/00 -0500, Tom Lane wrote:
>A brute-force answer would be to remove the url_url index ;-)
>dunno if that would slow down other queries, however.

Could you trick it into not using the index (AND using the other strategy?)
by using a calculation:

SELECT ndict.url_id,ndict.intag  FROM ndict,url WHERE ndict.word_id=1971739852   AND url.rec_id=ndict.url_id    AND (
(url.url|| ' ') LIKE 'http://www.postgresql.org/% ');
 

it's a bit nasty.

If you had 7.1, the following might work:

SELECT url_id,intag From  (Select ndict.url_id,ndict.intag,url  FROM ndict,url WHERE ndict.word_id=1971739852   AND
url.rec_id=ndict.url_id)as zzz
 
Where    zzz.url LIKE 'http://www.postgresql.org/%'

But I don't know how subselect-in-from handles this sort of query - it
might be 'clever' enough to fold it somehow.




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