Weird NOT IN effect with NULL values

From: Frank Joerdens <frank(at)joerdens(dot)de>
To: pgsql-sql(at)postgresql(dot)org
Subject: Weird NOT IN effect with NULL values
Date: 2001-03-01 18:16:54
Message-ID: 20010301191654.A12406@rakete.joerdens.de
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When doing a subselect with NOT IN, as in

SELECT name
FROM customer
WHERE customer_id NOT IN (
SELECT customer_id
FROM salesorder
);

(from Bruce Momjian's book)

I get no rows if the result column returned by the subselect
contains NULL values. It works as expected if I remove the NULL values
from the result set. Is this behaviour correct and if so, why?

I am using 7.1 beta 4.

Regards, Frank

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