SQL加入三个表

Question

我有三个表：Cutomers，Orders和Items，其中包含一些数据

表：项目

Id   Name  Order_Id         price
----------------------------------
1   Item1   1               10
2   Item2   1               20
3   Item3   2               30
4   Item4   2               40
5   Item5   3               50
6   Item6   3               60
7   Item7   4               70
8   Item8   5               80
9   Item9   5               90

表：订单

Id     Customer_Id
----------------------
1       1
2       1
3       2
4       2
5       3
-----------------------

表：客户

Id   Name
------------------------
1   Alex
2   John
3   Mark
-------------------------

我希望SQl查询输出结果为

------------------------------------------
Name    Total    Total      Total
        Order    Orders     Items
        Price
--------------------------------------------
Alex    100        2         4
John    180        2         3
Mark    170        1         2
----------------------------------------

我尝试使用以下查询＆gt;＆gt;＆gt;＆gt;＆gt;＆gt;＆gt;＆gt;＆gt;＆gt;＆gt;＆gt;＆gt;

Select c.Name, SUM(i.price) as 'Total Order Price', COUNT(o.Id) as 
'Total   Orders' ,COUNT(i.id) as 'Total Items'
from Customers c  
left join Orders o  
on o.Customer_Id=c.Id
left join Items i
on i.Order_Id=o.Id 
group by c.Name 

Out Put：＆gt;＆gt;＆gt;＆gt;＆gt;＆gt;＆gt;＆gt;＆gt;＆gt;＆gt;＆gt;＆gt;＆gt;

Name    Total    Total      Total
        Order    Orders     Items
        Price
--------------------------------------------
Alex    100        4         4
John    180        3         3
Mark    170        2         2
----------------------------------------    

Answer 1

对于您的查询，最简单的解决方案是使用Date tgl = rs.getDate("Tanggal_Lahir");//take from database Date kini = new Date(); int umur = kini.getYear()-tgl.getYear();//.getyear have strikethrough ：

count(distinct)

不要使用单引号作为列别名。这会引起混淆，因为它仅适用于Select c.Name, SUM(i.price) as TotalOrderPrice, COUNT(DISTINCT o.Id) as TotalOrders, COUNT(i.id) as TotalItems from Customers c left join Orders o on o.Customer_Id = c.Id left join Items i on i.Order_Id = o.Id group by c.Name ; 之后的select。将列命名为不需要转义字符的字符串，或者为数据库使用适当的转义字符（通常是双引号，方括号或后标记）。

Answer 2

我建议使用下面的查询，它只使用内连接而不是左连接：

SELECT c.name, SUM(i.price), COUNT(DISTINCT order_id), COUNT(DISTINCT i.id)  
FROM items i
     JOIN orders o ON i.order_id = o.id
     JOIN customers c ON c.id = o.customer_id
GROUP BY c.name;

我希望它有所帮助。