Repeat rows in the result based on an integer value in column - mysql

Question

I have following table.
Sales:
id quantity price_charged
------------------------------
101 2 100
102 3 300
103 1 120
I want to select the records such that it repeat Rows N time according to quantity column value.
So I need following results
id quantity price_charged
--------------------------------
101 1 50
101 1 50
102 1 100
102 1 100
102 1 100
103 1 120

Answer 1

I think, it is better to resolve not with query(SQL).
There is some generation feature, but its performance is poor.
You have to change your model(store always 1 quantity), or process it in backend(java/c/stb.)
Select id,
1 as quantity,
price_charged
from table_name t
JOIN
(SELECT e*10000+d*1000+c*100+b*10+a n FROM
(select 0 a 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) t1,
(select 0 b 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) t2,
(select 0 c 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) t3,
(select 0 d 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) t4,
(select 0 e 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) t5) counter
ON (counter.n<=t.quantity)
The joined subquery reapeted numbers from 0 to 99999 it is the burn it maximum for quantity. The join repeat by the counter 0... quantity-1 values.

Answer 2

I was able to come up with a solution for my problem after referring an answer for how to generate series in mysql. Here is the link.
SELECT
sal.id,
1 as quantity, sal.quantity as originalQty,
sal.price_charged/sal.quantity
FROM
(SELECT
#num := #num + 1 AS count
FROM
sales, -- this can be any table but it should have row count
-- more than what we expect the max value of Sales.quantity column
(SELECT #num := 0) num
LIMIT
100) ctr
JOIN sales sal
ON sal.quantity >= ctr.count
order by id;

Answer 3

If you are lucky enough to be running MySQL 8.0, you can use a recursive CTE to solve this problem. This is an elegant solution that does not require creating a list of numbers of using variables.
Consider this query:
WITH RECURSIVE cte AS (
SELECT 1 n, id, quantity, price_charged FROM sales
UNION ALL
SELECT n + 1, id, quantity, price_charged FROM cte WHERE n < quantity
)
SELECT id, quantity, price_charged/quantity quantity
FROM cte
ORDER BY id;
In this DB Fiddle with your sample data, the query returns:
| id | quantity | quantity |
| --- | -------- | -------- |
| 101 | 2 | 50 |
| 101 | 2 | 50 |
| 102 | 3 | 100 |
| 102 | 3 | 100 |
| 102 | 3 | 100 |
| 103 | 1 | 120 |