如何計算 SQL (Access, JetSQL) 中兩個 SELECT 的差異

Question

我需要從同一個表連接中獲取兩個SUM...WHERE查詢的區別：

SELECT SUM(Service_template.Service_fee)
FROM (Service_template LEFT JOIN Service ON Service_template.Service_Code = Service.Service_Code) LEFT JOIN Bill ON Service.Service_ID = Bill.Service_ID
WHERE Bill.Service_ID IS NOT NULL

和

SELECT SUM(Service_template.Service_fee)
FROM (Service_template LEFT JOIN Service ON Service_template.Service_Code = Service.Service_Code) LEFT JOIN Bill ON Service.Service_ID = Bill.Service_ID

我試過使用UNION ，但它返回兩行，而不是我可以進行計算的兩列。

我該怎么做go呢？ 我覺得我錯過了一些微不足道的東西，所以提前謝謝！

Answer 1

這應該有效：

Select
  Sum(T1.Sum1),
  Sum(T2.Sum2),
  Sum(T1.Sum1) - Sum(T2.Sum2) As Diff1,
  Sum(T2.Sum2) - Sum(T1.Sum1) As Diff2
From
  (SELECT SUM(Service_template.Service_fee) As Sum1 FROM (Service_template LEFT JOIN Service ON Service_template.Service_Code = Service.Service_Code) LEFT JOIN Bill ON Service.Service_ID = Bill.Service_ID WHERE Bill.Service_ID IS NOT NULL) As T1,
  (SELECT SUM(Service_template.Service_fee) As Sum2 FROM (Service_template LEFT JOIN Service ON Service_template.Service_Code = Service.Service_Code) LEFT JOIN Bill ON Service.Service_ID = Bill.Service_ID) As T2

Answer 2

如果你想要所有三個值，你可以使用條件聚合：

SELECT SUM(IIF(b.Service_ID IS NOT NULL, st.Service_fee, 0)) as total_1,
       SUM(b.Service_Id) as total_2,
       SUM(IIF(b.Service_ID IS NULL, st.Service_fee, 0)) as diff      
FROM (Service_template as st LEFT JOIN
      Service as s
      ON st.Service_Code = s.Service_Code
     ) LEFT JOIN
     Bill as b
     ON s.Service_ID = b.Service_ID;

如果您只想要Service_Id為NULL的SUM() ，那么：

SELECT SUM(b.Service_Id) as diff      
FROM (Service_template as st LEFT JOIN
      Service as s
      ON st.Service_Code = s.Service_Code
     ) LEFT JOIN
     Bill as b
     ON s.Service_ID = b.Service_ID
WHERE b.Service_ID IS NULL;