如何簡化下面的SQL查詢？

Question

如何簡化下面的SQL查詢，

DECLARE @EMPLOYEE1 TABLE (EMPID INT,DEPT1 INT,DEPT2 INT) 
DECLARE @EMPLOYEE2 TABLE (EMPID INT,DEPT1 INT,DEPT2 INT) 

    INSERT INTO @EMPLOYEE1 VALUES 
    (1,1,1), 
    (2,2,2), 
    (3,10,3), 
    (4,4,4) 
    INSERT INTO @EMPLOYEE2 VALUES 
    (1,1,1), 
    (2,2,2), 
    (3,10,10), 
    (4,10,4)  

    SELECT A.EMPID,  
      A.DEPT1 EMP1_DEPT, 
      0 TYPES 
    FROM @EMPLOYEE1 A 
    LEFT JOIN @EMPLOYEE2 B ON A.DEPT1=B.DEPT1 
    WHERE B.DEPT1 IS NULL 

    UNION ALL 

    SELECT A.EMPID,  
      A.DEPT2 EMP2_DEPT, 
      1 TYPES 
    FROM @EMPLOYEE1 A 
    LEFT JOIN @EMPLOYEE2 B ON A.DEPT2=B.DEPT2 
    WHERE B.DEPT2 IS NULL 

任何一個可以排序這個問題，在此先感謝

Answer 1

下面是做到這一點的一種方法：是另一種選擇使用

SELECT DISTINCT 
     A.EMPID,  
     CASE WHEN B.DEPT1 IS NULL THEN A.DEPT1 ELSE A.DEPT2 END As EMP1_DEPT, 
     CASE WHEN B.DEPT1 IS NULL THEN 0 ELSE 1 END As TYPES 
FROM @EMPLOYEE1 A 
LEFT JOIN @EMPLOYEE2 B ON A.DEPT1=B.DEPT1 
LEFT JOIN @EMPLOYEE2 C ON A.DEPT2=C.DEPT2 
WHERE B.DEPT1 IS NULL 
OR C.DEPT2 IS NULL 

Answer 2

這裏CROSS APPLY和VALUES：

SELECT A.EMPID, 
     A_D.DEPT AS 'EMP1_DEPT', 
     A_D.[TYPES] 
FROM @EMPLOYEE1 A 
CROSS APPLY (VALUES (A.DEPT1, 0), (A.DEPT2, 1)) A_D (DEPT, [TYPES]) 
WHERE NOT EXISTS (SELECT 1 
        FROM @EMPLOYEE2 B 
        CROSS APPLY (VALUES (B.DEPT1, 0), (B.DEPT2, 1)) B_D (DEPT, [TYPES]) 
        WHERE B_D.DEPT = A_D.DEPT 
        AND B_D.[TYPES] = A_D.[TYPES]); 

這種方法的優點是每個表只被命中一次。它使用NOT EXISTS通過使用左反半連接來提高查詢計劃中的性能。