MySQL stored procedure, while loop, union dataset - mysql

Question

I'm new to stored procedures so I may be doing this wrong. I've created a stored procedure that brings back month name, month start and month end but I'm getting 12 separate datasets.
How can I combine this into one?
BEGIN
SET #i = 0;
SET #start_date = "2018-09-01";
SET #end_date = LAST_DAY('2018-09-01');
WHILE #i < 12 DO
SELECT MONTHNAME(#start_date) AS month, #start_date, #end_date;
SET #i = #i + 1;
SET #start_date = DATE_ADD(#start_date, INTERVAL 1 MONTH);
SET #end_date = LAST_DAY(DATE_ADD(#end_date, INTERVAL 1 MONTH));
END WHILE;
END

Answer 1

You don't need a stored procedure for that.
set #start_date = '2018-09-01';
with recursive months(m) as (
select 0
union all
select m + 1
from months
where m < 11
)
select #start_date + interval m.m month as first_day
, last_day(#start_date + interval m.m month) as last_day
from months m
order by m.m asc
Result:
first_day last_day
2018-09-01 2018-09-30
2018-10-01 2018-10-31
2018-11-01 2018-11-30
2018-12-01 2018-12-31
2019-01-01 2019-01-31
2019-02-01 2019-02-28
2019-03-01 2019-03-31
2019-04-01 2019-04-30
2019-05-01 2019-05-31
2019-06-01 2019-06-30
2019-07-01 2019-07-31
2019-08-01 2019-08-31
But you can ofcourse use that query in your SP too.

Answer 2

Rewrote #Paul Spiegel query so that I can understand how recursive queries work.
SET #start = "2018-09-01";
WITH RECURSIVE months (m)
AS (
SELECT 0
UNION ALL
SELECT m + 1
FROM months
WHERE m < 12
)
SELECT
MONTHNAME(DATE_ADD(#start, INTERVAL m MONTH)) AS month_name,
CONCAT(DATE_ADD(#start, INTERVAL m MONTH), " 00:00:00") AS start_of_month,
CONCAT(LAST_DAY(DATE_ADD(#start, INTERVAL m MONTH)), " 23:59:59") AS end_of_month
FROM months;

Answer 3

For MySQL versions before 8.0 , we can do something like this:
SELECT MONTHNAME(d.dt + INTERVAL i.n MONTH) AS month
, d.dt + INTERVAL i.n MONTH AS start_date
, LAST_DAY(d.dt + INTERVAL i.n MONTH) AS end_date
FROM ( SELECT '2018-09-01' + INTERVAL 0 MONTH AS dt ) d
CROSS
JOIN ( 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 UNION ALL SELECT 10 UNION ALL SELECT 11
) i
ORDER
BY i.n