SQL - 如何加入两个表并根据它们之间的 ID 对列求和？

Question

我有两张桌子。一张表是主数据

表 tbl1：

+-------------+------------+------------+
| ID          | Name       | Total      | 
+-------------+------------+------------+
| 1           | a          | 10         |
| 2           | b          | 5          |
| 3           | c          | 4          |
| 4           | a          | 4          |
+-------------+------------+------------+

第二个表tbl2 包含子数据。表之间的键是ID

表 tbl2：

+-------------+------------+
|id           | qty        | 
+-------------+------------+
| 1           | 4          |              
| 1           | 3          |                
| 1           | 1          |                
| 3           | 1          |                
| 3           | 3          |                
+-------------+------------+

我需要得到这样的输出：

输出：

+-------------+------------+------------+
| name        | sum_tot    | sum_qty    | 
+-------------+------------+------------+
| a           | 14         | 8          |
| b           | 5          | 0          |
| c           | 4          | 4          |
+-------------+------------+------------+

我试过这个：

select tbl1.name, SUM(tbl1.total), SUM(tbl2.qty)
from tbl1
left join tbl2 ON tbl1.id = tbl2.id
GROUP by tbl1.name

我得到的输出是：

输出：

+-------------+------------+------------+
| name        | sum_tot    | sum_qty    | 
+-------------+------------+------------+
| a           | 34         | 8          |
| b           | 5          |null        |
| c           | 8          | 4          |
+-------------+------------+------------+

这是不正确的。

这里是sql fiddle：

第一个表的摘要与第二个表无关。似乎以某种方式查询运行了 3 次。

Answer 1

您可以简单地拥有一个计算 tbl2 总和的相关子查询：

select tbl1.name, 
       SUM(tbl1.total), 
       SUM(COALESCE((select SUM(tbl2.qty) 
                     from tbl2
                     where tbl1.id = tbl2.id), 0)) as qty_tot
from tbl1
GROUP by tbl1.name

Answer 2

SELECT A.name, SUM(A.total) as sum_tot, COALESCE(B.sum_qty, 0) as sum_qty
FROM tbl1 A
LEFT JOIN (
    SELECT id, SUM(qty) as sum_qty
    FROM tbl2
    GROUP BY id
) B ON B.id = A.id
GROUP BY A.name

Answer 3

select tbl1.name, SUM(tbl1.total), SUM(COALESCE(tbl2.qty, 0))
from tbl1
left join tbl2 ON tbl1.id = tbl2.id
GROUP by tbl1.name