Select a row for each 'quantity' - mysql

Question

Table:
Article | Quantity | pricePerUnit | order_id | article_id
--------|----------|--------------------------------------
14 | 2 | 10.0 | 1 | 1
X1 | 1 | 5.0 | 1 | 2
Expected output:
Article | Quantity | pricePerUnit | order_id
--------|----------|------------------------
14 | 1 | 10.0 | 1
14 | 1 | 10.0 | 1
X1 | 1 | 5.0 | 1
What is a fast SELECT to populate the resultset with 1 row for each quantity per article?
Sorry I didn't try anything, I'm not sure wether this is possible at all. Self join.. would not be a help, grouping functions,..
Maybe GROUP BY order_id, article_id, quantity somehow..

Answer 1

UPDATE: For the max quantity of three just do
SELECT Article, 1 Quantity, pricePerUnit, order_id
FROM articles a JOIN
(
SELECT 1 AS n UNION ALL
SELECT 2 UNION ALL
SELECT 3
) n
ON n.n <= a.Quantity
ORDER BY order_id, Article
Here is SQLFiddle demo
Original answer: You can try
SELECT Article, 1 Quantity, pricePerUnit, order_id
FROM articles a JOIN
(
SELECT a.N + b.N * 10 + 1 n
FROM
(SELECT 0 AS N UNION ALL SELECT 1 UNION ALL SELECT 2 UNION ALL SELECT 3 UNION ALL SELECT 4 UNION ALL SELECT 5 UNION ALL SELECT 6 UNION ALL SELECT 7 UNION ALL SELECT 8 UNION ALL SELECT 9) a
,(SELECT 0 AS N UNION ALL SELECT 1 UNION ALL SELECT 2 UNION ALL SELECT 3 UNION ALL SELECT 4 UNION ALL SELECT 5 UNION ALL SELECT 6 UNION ALL SELECT 7 UNION ALL SELECT 8 UNION ALL SELECT 9) b
) n
ON n.n <= a.Quantity
ORDER BY order_id, Article
An inner select returns 100 rows meaning you can unpivot quantities up to the value of 100. If you need more update it accordingly.
Here is SQLFiddle demo
Given that it is for a report and you have necessary right to create a new table it's best to substitute an inner select with a tally (numbers) table which you can create in the same manner:
CREATE TABLE tally (n int not null auto_increment primary key);
INSERT INTO tally
SELECT a.N + b.N * 10 + 1 n
FROM
(SELECT 0 AS N UNION ALL SELECT 1 UNION ALL SELECT 2 UNION ALL SELECT 3 UNION ALL SELECT 4 UNION ALL SELECT 5 UNION ALL SELECT 6 UNION ALL SELECT 7 UNION ALL SELECT 8 UNION ALL SELECT 9) a
,(SELECT 0 AS N UNION ALL SELECT 1 UNION ALL SELECT 2 UNION ALL SELECT 3 UNION ALL SELECT 4 UNION ALL SELECT 5 UNION ALL SELECT 6 UNION ALL SELECT 7 UNION ALL SELECT 8 UNION ALL SELECT 9) b
ORDER BY n;
And then your query will look like
SELECT Article, 1 Quantity, pricePerUnit, order_id
FROM articles a JOIN tally n
ON n.n <= a.Quantity
ORDER BY order_id, Article
Here is SQLFiddle demo