From: | Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us> |
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To: | Alvaro Herrera <alvherre(at)alvh(dot)no-ip(dot)org> |
Cc: | Dave Cramer <pg(at)fastcrypt(dot)com>, postgresql performance list <pgsql-performance(at)postgresql(dot)org> |
Subject: | Re: difference between a unique constraint and a unique index ??? |
Date: | 2007-11-12 16:37:14 |
Message-ID: | 6836.1194885434@sss.pgh.pa.us |
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Lists: | pgsql-performance |
Alvaro Herrera <alvherre(at)alvh(dot)no-ip(dot)org> writes:
> Well, AFAIK the index with varchar_pattern_ops is used for LIKE queries,
> whereas the other one is going to be used for = queries. So you need to
> keep both indexes.
Given the current definition of text equality, it'd be possible to drop
~=~ and have the standard = operator holding the place of equality in
both the regular and pattern_ops opclasses. Then it'd be possible to
support regular equality queries, as well as LIKE, with only the
pattern_ops index.
This would break any applications explicitly using ~=~, but how many
of those are there?
(For backwards compatibility it'd be nice if we could allow both = and
~=~ in the opclass, but the unique index on pg_amop seems to preclude
that.)
regards, tom lane
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