NULL handling in EXCEPT

Question

Accepted Answer

EXCEPT uses the same NULL-equality rule as all set operations: two NULLs are considered identical. The NULL in source matches the NULL in exclusions, so it is removed from the result. Only 10 survives because it does not appear in exclusions. This is the opposite of a WHERE v <> exclusions.v filter, where the NULL comparison would produce UNKNOWN and the NULL row would slip through.