When is `x IS NOT NULL` not the same as `NOT(x IS NULL)`

Posted by Mark Hurd on Stack Overflow See other posts from Stack Overflow or by Mark Hurd
Published on 2010-05-18T16:29:55Z Indexed on 2010/05/18 16:40 UTC
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null

For what x is

The expression x IS NOT NULL is not equal to NOT(x IS NULL), as is the case in 2VL

(quote from this answer, which is quoting Fabian Pascal Practical Issues in Database Management - A Reference for the Thinking Practitioner -- near the end of that answer)

My guess is when x IS NULL is NULL, but I cannot guess when that would be (i.e. I haven't checked the SQL standard).

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