From: | Doug McNaught <doug(at)wireboard(dot)com> |
---|---|
To: | "P(dot) Dwayne Miller" <dmiller(at)espgroup(dot)net> |
Cc: | PostgreSQL Hackers Newsgroup <pgsql-hackers(at)postgresql(dot)org> |
Subject: | Re: select count... |
Date: | 2001-07-13 13:16:35 |
Message-ID: | m3n169x93g.fsf@belphigor.mcnaught.org |
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"P. Dwayne Miller" <dmiller(at)espgroup(dot)net> writes:
> What's the fastest way to select the number of rows in a table? If I
> use count(*) with no whereclause, it uses a seq_scan and takes 4 secs
> (122k rows). With a where clause, it uses an index and returns in < 1
> sec. Selecting count(requestnumber), which is an indexed column, with
> no where clause again takes 4 secs. This latter version, I thought,
> would use the index. The values of requestnumber are very distributed.
Exactly how would you expect to get a count of all the rows in the
table (no WHERE clause) without a sequential scan? I don't see any
problem with the above results.
The only case in which COUNT(requestnumber) might use the index would
be if there were a significant number of NULLs in that column, but you
don't give any information on that.
-Doug
--
The rain man gave me two cures; he said jump right in,
The first was Texas medicine--the second was just railroad gin,
And like a fool I mixed them, and it strangled up my mind,
Now people just get uglier, and I got no sense of time... --Dylan
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