SQL Query Expanding Each Row Every Int. In Range Between COL_A and COL_B - sql

Question

My SQL Server has a TABLE. Both columns are integers, but represent dates in the form YYYYMM. I'd like to query this table and return a third column which, for every row, includes an integer in the form of YYYYMM for every year/month in the range of the two columns.
Here's the TABLE:
+------------+------------+
| beg_YYYYMM | end_YYYYMM |
+------------+------------+
| 201802 | 201805 |
| 201711 | 201801 |
+------------+------------+
Desired output:
+------------+------------+----------------+
| beg_YYYYMM | end_YYYYMM | month_in_range |
+------------+------------+----------------+
| 201802 | 201805 | 201802 |
| 201802 | 201805 | 201803 |
| 201802 | 201805 | 201804 |
| 201802 | 201805 | 201805 |
| 201711 | 201801 | 201711 |
| 201711 | 201801 | 201712 |
| 201711 | 201801 | 201801 |
+------------+------------+----------------+

Answer 1

Use a recursive CTE:
with cte as (
select beg_YYYYMM, end_YYYYMM,
convert(date, convert(varchar(255), beg_YYYYMM) + '01') as dte,
convert(date, convert(varchar(255), end_YYYYMM) + '01') as end_dte
from t
union all
select beg_YYYYMM, end_YYYYMM,
dateadd(month, 1, dte),
end_dte
from cte
where dte < end_dte
)
select beg_yyyymm, end_yyyymm,
year(dte) * 100 + month(dte) as yyyymm
from cte
order by dte;
Here is a db<>fiddle.

Answer 2

I really don't think I would actually deploy this but I wanted to know what it would look like. If you create a TVF that does the ugly work it isn't too bad. I used Aaron Bertrand's DateDim code with a quick modification to just get first of the month dates between the two dates that are passed in.
CREATE OR ALTER FUNCTION dbo.tvf_MonthRange (#beg_YYYYMM int, #end_YYYYMM int)
RETURNS #Results TABLE
(month_in_range int)
AS
BEGIN
--Have to convert ints to dates
DECLARE #BegDate DATE;
SET #BegDate = DATEFROMPARTS(CAST(SUBSTRING(CAST(#beg_YYYYMM AS varchar(6)),1,4) AS INT), CAST(SUBSTRING(CAST(#beg_YYYYMM AS varchar(6)),5,2) AS INT), 1);
--This needs to be the second day of the month for the code below to work.
DECLARE #EndDate DATE;
SET #EndDate = DATEFROMPARTS(CAST(SUBSTRING(CAST(#end_YYYYMM AS varchar(6)),1,4) AS INT), CAST(SUBSTRING(CAST(#end_YYYYMM AS varchar(6)),5,2) AS INT), 2);
INSERT INTO #Results
SELECT (DATEPART(YEAR, d) *100) + DATEPART(MONTH, d)
FROM
(
SELECT d = DATEADD(DAY, rn - 1, #BegDate)
FROM
(
SELECT TOP (DATEDIFF(DAY, #BegDate, #EndDate))
rn = ROW_NUMBER() OVER (ORDER BY s1.[object_id])
FROM sys.all_objects AS s1
CROSS JOIN sys.all_objects AS s2
-- on my system this would support > 5 million days
ORDER BY s1.[object_id]
) AS x
) AS y
WHERE DATEPART(DAY, d) = 1;
RETURN;
END
Then you can call it like this.
DECLARE #Months TABLE (beg_YYYYMM int, end_YYYYMM int)
INSERT INTO #MONTHS SELECT 201802, 201805
INSERT INTO #MONTHS SELECT 201711, 201801
SELECT *
FROM #Months m
CROSS APPLY dbo.tvf_MonthRange(m.beg_YYYYMM, m.end_YYYYMM) mr ;
It is bad idea Monday right?

Answer 3

A solution using a tally table which may be faster on larger data sets.
with dates as(
select
201501 as beg_YYYYMM
,201504 as end_YYYYMM
union all
select '201711', '201801'
union all
select '201807', '201812'
),
--Tally table
ctedaterange AS (
SELECT top 15
rn = Row_number() OVER(ORDER BY (SELECT NULL)) -1
FROM sys.objects a
)
SELECT
dates.*
,months_in_range = convert(varchar(6), Dateadd(mm, rn, cast(cast(dates.beg_YYYYMM as varchar(8)) +'01' as date)), 112)
FROM dates
cross join ctedaterange
WHERE
rn <= Datediff(mm, cast(cast(dates.beg_YYYYMM as varchar(8)) +'01' as date), cast(cast(dates.end_YYYYMM as varchar(8)) +'01' as date))
ORDER BY
beg_YYYYMM
,Dateadd(mm, rn, cast(cast(dates.beg_YYYYMM as varchar(8)) +'01' as date))
Here's the db<>fiddle