Re: Weird NOT IN effect with NULL values

Mr. Joerdens,

> 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 can see how that bug would happen.  You may want to forward your
e-mail to pgsql-bugs.

Regardless, you'll find that you get faster results (as well as avoiding
the NULL bug) if you use the following form of the query:

SELECT name
FROM customer
WHERE NOT EXISTS (
SELECT customer_id
FROM salesorder
WHERE customer_id = customer.customer_id
);

Bruce, you may want to consider editing your next edition to include the
above modification.  WHERE ... NOT IN is a bad idea for any subselect on
medium-large tables.

-Josh Berkus


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