SQL/MySQL: split a quantity value into multiple rows by date - mysql

Question

I have a table with three columns: planning_start_date - planning_end_date - quantity.
For example I have this data:
planning_start_date | planning_end_date | quantity
2019-03-01 | 2019-03-31 | 1500
I need to split the value 1500 into multiple rows with the adverage per day, so 1500 / 31 days = 48,38 per day.
The expected result should be:
date daily_qty
2019-03-01 | 48,38
2019-03-02 | 48,38
2019-03-03 | 48,38
...
2019-03-31 | 48,38
Anyone with some suggestions?

Answer 1

Should you decide to upgrade to MySQL 8.0, here's a recursive CTE that will generate a list of all the days between planning_start_date and planning_end_date along with the required daily quantity:
WITH RECURSIVE cte AS (
SELECT planning_start_date AS date,
planning_end_date,
quantity / (DATEDIFF(planning_end_date, planning_start_date) + 1) AS daily_qty
FROM test
UNION ALL
SELECT date + INTERVAL 1 DAY, planning_end_date, daily_qty
FROM cte
WHERE date < planning_end_date
)
SELECT `date`, daily_qty
FROM cte
ORDER BY `date`
Demo on dbfiddle

Answer 2

In MySLQ 8+, you can use a recursive CTE like this:
with recursive cte(dte, planning_end_date, quantity, days) as (
select planning_start_date as dte, planning_end_date, quantity, datediff(planning_end_date, planning_start_date) + 1 as days
from t
union all
select dte + interval 1 day as dte, planning_end_date, quantity, days
from cte
where dte < planning_end_date
)
select dte, quantity / days
from cte;
Here is a db<>fiddle.
In earlier versions, you want a numbers table of some sort. For instance, if your table has enough rows, you can just use it:
select (planning_start_date + interval n.n day),
quantity / (datediff(planning_end_date, planning_start_date) + 1)
from t join
(select (#rn := #rn + 1) as n
from t cross join
(select #rn := 0) params
) n
on planning_start_date + interval n.n day <= planning_end_date;
You can use any table that is large enough for n.