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by int_19h
518 days ago
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SQL NULL is not "exactly equivalent" to unknown. E.g. in an outer join, there's nothing unknown about the result that is missing a row from one side, yet SQL semantics is to fill it with nulls. In practice, it behaves as "unknown" in some contexts, as "missing value" in other contexts, and sometimes it's just plain WTF like SUM() returning NULL rather than 0 if there are no rows. |
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