[서브쿼리] 예제 문제 Shipper_ID 총합 칼럼 추가 방법 문의

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스스로 정답을 찾아서 내용 공유합니다!

WITH(임시 테이블)라는 것을 사용하여 해결할 수 있었네요.

With Temp_table as
(
SELECT C.CustomerID, 
IFNULL(O1.ShipperID_1, 0) AS S1,
IFNULL(O2.ShipperID_2, 0) AS S2,
IFNULL(O3.ShipperID_3, 0) AS S3
FROM Customers AS C

LEFT JOIN (

SELECT CustomerID, Count(OrderID) AS ShipperID_1
FROM Orders
WHERE ShipperID = 1
Group By CustomerID

) AS O1
ON O1.CustomerID = C.CustomerID

LEFT JOIN (

SELECT CustomerID, Count(OrderID) AS ShipperID_2
FROM Orders
WHERE ShipperID = 2
Group By CustomerID

) AS O2
ON O2.CustomerID = C.CustomerID

LEFT JOIN (

SELECT CustomerID, Count(OrderID) AS ShipperID_3
FROM Orders
WHERE ShipperID = 3
Group By CustomerID

) AS O3
ON O3.CustomerID = C.CustomerID
)
Select CustomerID, S1, S2, S3, S1+S2+S3 AS SUM
From Temp_table