mysql我想操纵两个表之间的数据

Question

我有一张生产表：

--------  ---------
| Items | quantity | 
--------  ---------
| A     |   100    |
--------------------
| B     |   30     |
--------------------
| A     |   10     |
--------------------
| C     |   80.    |
--------------------

表销售

--------  ---------
| Items | quantity | 
--------  ---------
| A     |   50    |
--------------------
| C     |   30     |
--------------------

必填结果

--------  ---------
| Items | quantity | 
--------  ---------
| A     |   60    |
--------------------
| B    |   30     |
--------------------
| C     |   50     |
--------------------

我正在尝试使用外连接，但无法成功。请帮帮我。 感谢

Answer 1

select p.items, sum(p.quantity) - coalesce(max(total_quantity), 0)
from production p
left join 
(
    select items, sum(quantity) as total_quantity
    from sale
    group by items
) s on s.items = p.items
group by p.items

Answer 2

select p.Items, SUM(IFNULL(p.quantity,0))-SUM(IFNULL(s.quantity,0)) 
FROM production p 
left join sale s 
on p.items = s.items 
group by p.items

编辑以防止空值。你为MySQL标记了两个不同的SQL数据库mysql和sql-server我相信它是IFNULL（如代码所示），而在sql-server中它是ISNULL