如何计算 SQL (Access, JetSQL) 中两个 SELECT 的差异

Question

我需要从同一个表连接中获取两个SUM...WHERE查询的区别：

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

我试过使用UNION ，但它返回两行，而不是我可以进行计算的两列。

我该怎么做go呢？ 我觉得我错过了一些微不足道的东西，所以提前谢谢！

Answer 1

这应该有效：

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

如果你想要所有三个值，你可以使用条件聚合：

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为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;