I got it wrong because I thought TWO NULL Values are NOT supposed to be same(identical). So I chose the option with 3 rows. Quirk of SQLServer?
No quirk. Expected behaviour, as required by the ANSI standard.
NULL values are considered to yield "unknown" (not false!) on any comparison predicate, so they are neither equal nor unequal. But that does not apply here. This is a grouping operation, and the ANSI standard explicitly states that NULL values are considered to be not distinct for grouping purposes.
Hugo Kornelis, SQL Server MVP
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