From: | Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us> |
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To: | "Chris Hoover" <revoohc(at)gmail(dot)com> |
Cc: | "pgsql-admin(at)postgresql(dot)org Admin" <pgsql-admin(at)postgresql(dot)org> |
Subject: | Re: any way to make query use index? |
Date: | 2007-11-15 16:25:24 |
Message-ID: | 3669.1195143924@sss.pgh.pa.us |
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Lists: | pgsql-admin |
"Chris Hoover" <revoohc(at)gmail(dot)com> writes:
> SELECT rev_desc FROM rev_code_desc WHERE rev_code = lpad('0300', 4, '0')
> Is there anyway to make postgres use an index on this query?
> Here is the table definition:
> CREATE TABLE rev_code_desc
> (
> rev_code character(4) NOT NULL,
Since rev_code is char(n), you need to cast the other thing to char(n)
as well:
SELECT rev_desc FROM rev_code_desc WHERE rev_code = lpad('0300', 4, '0')::char(4)
lpad() is declared to return text, which means that your original query
resolves as ... WHERE rev_code::text = lpad('0300', 4, '0'), which
means that the index on rev_code is useless (since it has bpchar
semantics not text semantics).
If changing the queries seems impractical, you could add an index on
rev_code::text, or reconsider the choice of column type.
regards, tom lane
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