Question

所以我试图找出每个客户在削减和产品上花费的总金额

我不知道我的查询是错的还是我的整个数据库架构有什么想法？

我的查询

`Select First_Name, SUM(B.Cost), SUM(C.Cost)
FROM bookings A, cuts B, products C, customers D
Where A.Customer_ID= D.Customer_ID
AND A.Cut_ID = B.Cut_ID
AND A.Product_ID= C.Product_ID;`

我的数据库

`Table: bookings 
Booking_N0, Customer_ID, Cut_ID, Product_ID, TimeTaken`


`Table: customers
Customre_ID, First_Name, Sex`


`Table: products
Product_ID, Products, Cost`

`Table: cuts
 Cut_ID, Cut, Cost`

Answer 1

每个客户都应该GROUP BY到SUM：

Select D.First_Name
     , SUM(B.Cost)
     , SUM(C.Cost)
FROM bookings A LEFT JOIN cuts B ON A.Cut_ID = B.Cut_ID
                JOIN products C ON A.Product_ID = C.Product_ID
                JOIN customers D ON A.Customer_ID = D.Customer_ID
GROUP BY D.First_Name;

此外，期待使用显式连接表示法（FROM table1 t1 JOIN table2 t2 ON t1.field1 = t2.field2）而不是隐式连接表示法（FROM table1 t1, table2 t2 WHERE t1.field1 = t2.field2），因为它有更多直观视图（表格列在它们加入的条件附近）。

Answer 2

开始使用推荐的JOIN / ON语法进行连接，而不是使用WHERE子句。您还需要GROUP BY子句

Select First_Name, SUM(B.Cost), SUM(C.Cost)
FROM bookings A
INNER JOIN cuts B
 ON A.Cut_ID = B.Cut_ID
INNER JOIN products C 
 ON A.Product_ID= C.Product_ID
INNER JOIN customers D
 ON  A.Customer_ID= D.Customer_ID
GROUP BY First_Name

Answer 3

如果使用SUM等聚合函数，则必须添加group by子句在你的情况下：

 ...
 AND A.Product_ID= C.Product_ID
 GROUP BY First_Name

SQL查询或表错误？

3 个答案: