Question

I have two tables: Issue and Return. Both tables have columns article_id, person_id and quantity. I need to subtract Return table from Issue table for one person and group the result by article name.

First select looks like this:

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

Second like this:

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

Question is, how do I subtract second select from the first (Return – Issue) to get a table like this:

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

The Quantity in the final result should be the number of remaining articles to be returned.

Answer 1

This may work:

(heavily edited – my first answer did not have a chance of working…)

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