SQL WHERE 在多对多或多对多空

Question

有谁知道简化这个 WHERE 表达式的方法？

WHERE        (
                    (@UserSpecialtyID in
                        (
                            SELECT      CharacteristicSpecialties_Id
                            FROM        ModalityVariantSpecialty
                            WHERE       ModalityVariants_Id = ModalityVariants.Id
                        )
                    ) 
                    OR 
                    NOT EXISTS
                        (
                            SELECT      CharacteristicSpecialties_Id
                            FROM        ModalityVariantSpecialty
                            WHERE       ModalityVariants_Id = ModalityVariants.Id
                        )
                ) 

Answer 1

WHERE (
        @UserSpecialtyID in
        (
           SELECT      COALESCE(CharacteristicSpecialties_Id, A.A)
           FROM        (SELECT @UserSpecialtyID A) A LEFT JOIN ModalityVariantSpecialty
           ON          ModalityVariants_Id = ModalityVariants.Id
        )
      )

如果 CharacteristicSpecialties_Id，这很有效是一个不可为空的字段。