如何从其他表中减去一个表和

Question

我有两个表：Issue和Return。两个表都有article_id，person_id和quantity列。我需要从Return表中为一个人减去Issue表，并按结果名称对结果进行分组。

首先选择如下：

SELECT Article.Name, SUM(Issue.Quantity)
FROM Issue LEFT JOIN Article ON (Issue.ArticleID = Article.ID)
WHERE Issue.PersonID = 2
GROUP BY Article.Name

ArticleName  |  Quantity
------------------------
Shoes        |  5
Coats        |  3
Hats         |  3

第二个像这样：

SELECT Article.Name, SUM(Return.Quantity)
FROM Return LEFT JOIN Article ON (Return.ArticleID = Article.ID)
WHERE Return.PersonID = 2
GROUP BY Article.Name

ArticleName  |  Quantity
------------------------
Shoes        |  3
Coats        |  2
Hats         |  0

问题是，如何从第一个（Return - Issue）中减去第二个选择以获得这样的表：

ArticleName  |  Quantity
------------------------
Shoes        |  2
Coats        |  1
Hats         |  3

最终结果中的数量应该是要退回的剩余物品的数量。

Answer 1

这可能有效：

（经过大量编辑 - 我的第一个答案没有机会工作......）

SELECT Article.Name
, (SELECT SUM(Issue.Quantity) FROM Issue WHERE Issue.ArticleID = Article.ID AND Issue.PersonID = 2)
- (SELECT SUM(Return.Quantity) FROM Return WHERE Return.ArticleID = Article.ID AND Return.PersonID = 2)
FROM Article