就您而言，您只需要OR
WHERe ( acting_to is null OR ( datediff(day, acting_from, acting_to) >= 90 AND acting_to >= '2010-10-01' ) )
一种情况是针对 值 ，而不是条件。条件在CASE表达式之外
例如
CASE WHEN SomeCol = 'a' THEN ColA WHEN SomeCol = 'c' THEN ColC ELSE ColBEND > 42
就您而言，您只需要OR
WHERe ( acting_to is null OR ( datediff(day, acting_from, acting_to) >= 90 AND acting_to >= '2010-10-01' ) )
一种情况是针对 值 ，而不是条件。条件在CASE表达式之外
例如
CASE WHEN SomeCol = 'a' THEN ColA WHEN SomeCol = 'c' THEN ColC ELSE ColBEND > 42
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