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Re: Problem (bug?) with like

From: Bruce Momjian <pgman(at)candle(dot)pha(dot)pa(dot)us>
To: Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us>
Cc: drheart(at)wanadoo(dot)es, Lista PostgreSql <pgsql-general(at)postgresql(dot)org>, pgsql-hackers(at)postgresql(dot)org
Subject: Re: Problem (bug?) with like
Date: 2001-12-28 18:35:41
Message-ID: (view raw, whole thread or download thread mbox)
Lists: pgsql-generalpgsql-hackers
> Bruce Momjian <pgman(at)candle(dot)pha(dot)pa(dot)us> writes:
> > But what about '%A%' vs. '%AC%'.  Seems the second is reasonably
> > different from the first the our optimizer may be fine with that.  Is it
> > only when the strings get longer that we lose specificity?
> Yeah, I don't think that the estimates are bad for one or two
> characters.  But the estimate gets real small real fast as you
> increase the number of match characters in the LIKE pattern.
> We need to slow that down some.

See my earlier email about the 50% idea for LIKE.  Do ordinary string
comparisons also have this problem?

  Bruce Momjian                        |
  pgman(at)candle(dot)pha(dot)pa(dot)us               |  (610) 853-3000
  +  If your life is a hard drive,     |  830 Blythe Avenue
  +  Christ can be your backup.        |  Drexel Hill, Pennsylvania 19026

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