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From: Alexander Turchin <[email protected]>
To: PostgreSQL Mailing List <[email protected]>
Subject: COUNTs don't add up
Date: Mon, 23 Jul 2001 15:32:04 -0400
Message-ID: <[email protected]> (raw)

Hello all,

I have a database where (I believe; the database was not made by me) one
of the columns contains only two values: A or B. When I count all the
rows in the database I get X; when I count the rows containing A or B in
that column I get X-2; when I count the rows containing neither A nor B
I get 0. Any explanation (hopefully, again, I am doing something wrong
:)?

The actual queries are found below.

Thanks!

Alex

aturchin=# SELECT COUNT(*) FROM homol_loclink
aturchin-# WHERE (species2 = 'Mus musculus') OR
aturchin-# (species2 = 'Rattus norvegicus');
 count
-------
  7110
(1 row)

aturchin=# SELECT COUNT(*) FROM homol_loclink;
 count
-------
  7112
(1 row)

aturchin=# SELECT COUNT(*) FROM homol_loclink
aturchin-# WHERE (species2 <> 'Mus musculus') AND
aturchin-# (species2 <> 'Rattus norvegicus');
 count
-------
     0
(1 row)

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