Query: optimize CASE statement - remove conditions that are never hit

[maumar]

CASE
        WHEN CAST(0 AS bit) THEN x
        ELSE y
    END

we can simply remove the WHEN block since it's condition is never met so the result would be just y

If all the WHEN blocks have been removed and there is no ELSE condition we can return NULL

[smitpatel]

@maumar - Is this already done?

[ranma42]

Yes, this should already be optimized by

efcore/src/EFCore.Relational/Query/SqlNullabilityProcessor.cs

Lines 525 to 532 in ecd6104

	else if (IsFalse(testCondition))
	{
	// if test evaluates to 'false' we can remove the WhenClause
	RestoreNonNullableColumnsList(currentNonNullableColumnsCount);
	RestoreNullValueColumnsList(currentNullValueColumnsCount);
	continue;
	}

EDIT: clauses whose test is NULL instead of FALSE are currently left in; I'm working on it.