Re: Impact of varchar/text in use of indexes

From: Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us>
To: Mike Moran <mike_moran(at)mac(dot)com>
Cc: PgSQL Performance ML <pgsql-performance(at)postgresql(dot)org>
Subject: Re: Impact of varchar/text in use of indexes
Date: 2004-03-11 19:02:11
Message-ID: 21844.1079031731@sss.pgh.pa.us
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Mike Moran <mike_moran(at)mac(dot)com> writes:
> Hi. I have two existing tables, A and B. A has a 'varchar(1000)' field
> and B has a 'text' field, each with btree indexes defined. When I do a
> join between these, on this field, it seems to a hash join, as opposed
> to using the indexes, as I might expect (I'm no postgres expert, btw).

> My question is: if I changed both fields to be text or varchar(1000)
> then would the index be used?

Probably not, and in any case your assumption is mistaken. Indexes are
not always the right way to join.

regards, tom lane

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