SQL的GroupBy和InnerJoin

Question

SELECT 
    C.SOId, Ser.TotalService, S.TotalSales 
FROM 
    salesorder C 
    INNER JOIN (SELECT SOId,SUM(charge) as TotalService FROM sales_serviceline GROUP BY SOId) Ser 
    ON C.SOId = Ser.SOId 
    INNER JOIN (SELECT SOId,SUM(PriceEach*qty) as TotalSales FROM salesline GROUP BY SOId) S 
    ON C.SOId = S.SOId 

說明： 一個SalesOrder有許多salesline的 一個SalesOrder有許多salesline服務的

因此，如果salesorder有saleslins & salesline_service那麼上面的查詢成功retrives是salesorder總量，但如果只有鹽線或只有銷售線服務銷售訂單不重試如何更改此查詢以獲取所有結果？

Answer 1

我認爲您在尋找一個LEFT JOIN。如果在Ser或S無行，那麼LEFT JOIN會讓TotalService或TotalSalesNULL

SELECT 
    C.SOId, Ser.TotalService, S.TotalSales 
FROM 
    salesorder C 
    LEFT JOIN (SELECT SOId,SUM(charge) as TotalService FROM sales_serviceline GROUP BY SOId) Ser 
    ON C.SOId = Ser.SOId 
    LEFT JOIN (SELECT SOId,SUM(PriceEach*qty) as TotalSales FROM salesline GROUP BY SOId) S 
    ON C.SOId = S.SOId 

如果你不想讓他們爲NULL。那麼你可以簡單的使用COALESCE()。像這樣：

SELECT 
    C.SOId, 
    COALESCE(Ser.TotalService,0) AS TotalService, 
    COALESCE(S.TotalSales,0) AS TotalSales 
FROM 
    salesorder C 
    LEFT JOIN (SELECT SOId,SUM(charge) as TotalService FROM sales_serviceline GROUP BY SOId) Ser 
    ON C.SOId = Ser.SOId 
    LEFT JOIN (SELECT SOId,SUM(PriceEach*qty) as TotalSales FROM salesline GROUP BY SOId) S 
    ON C.SOId = S.SOId