Как рассчитать разницу двух SELECT в SQL (Access, Jet SQL)

Question

Мне нужно получить разницу двух SUM...WHERE запросов из одной и той же таблицы:

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

и

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

Я пытался использовать UNION, но он возвращает две строки, а не два столбца, по которым я могу сделать вычисления.

Как мне go сделать это? Я чувствую, что упускаю что-то тривиальное, поэтому заранее спасибо!

Answer 1

Если вам нужны все три значения, вы можете использовать условное агрегирование:

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;

Если вы просто хотите SUM(), где Service_Id равно NULL, тогда:

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;

Answer 2

Это должно работать:

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