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Message Posted: Mon, 24 Sep 2012 @ 20:06:21 GMT

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Subj:   Re: In where condition 'not' and 'and is not working together
From:   Pluebell, Fred

Your issue is 3-value logic, i.e. how NULL is handled. In particular, comparing NULL with another value (even another NULL) yields NULL as the result. To test for NULL you must use IS NULL (or IS NOT NULL). In the example:

not(100=100 and '1'='1') -> not (True and True) -> not (True) -> False

not(NULL=100 and '1'='1') -> not(NULL and True) -> not(NULL) -> NULL; but since this is final result, treated as False

not(NULL=100 and NULL='1') -> not(NULL and NULL) -> not(NULL) -> NULL; treated as False

not(NULL=NULL and '2'='1') -> not(NULL and False) -> not(False) -> True

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