Possible Duplicate:
SQL NOT IN constraint and NULL values
Why is following query not returning hello?
select 'hello' where 'a' not in ('b', null)
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Novice Developer
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Ref http://stackoverflow.com/questions/296146/sql-query-question-select-not-in – Salil Jun 25 '10 at 06:03
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Your query can be expanded to:
SELECT 'hello' WHERE 'a' <> 'b' AND 'a' <> NULL;
The first condition evaluates to true.
The second condition evaluates to neither true nor false because NULL is neither equal nor unequal to anything. The full WHERE clause is then: "true AND neither true nor false".
mechanical_meat
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I think you meant: the first condition evaluates to TRUE, but the second doesn't, so the AND becomes FALSE. – egrunin Jun 25 '10 at 08:26
