TSQL - Missing Month - sql-server

Question

I need to find the missing months in a table
for the earliest and latest start dates per ID_No. As an example:
create table #InputTable (ID_No int ,OccurMonth datetime)
insert into #InputTable (ID_No,OccurMonth)
select 10, '2007-11-01' Union all
select 10, '2007-12-01' Union all
select 10, '2008-01-01' Union all
select 20, '2009-01-01' Union all
select 20, '2009-02-01' Union all
select 20, '2009-04-01' Union all
select 30, '2010-05-01' Union all
select 30, '2010-08-01' Union all
select 30, '2010-09-01' Union all
select 40, '2008-03-01'
For the above table, the answer should be:
ID_No OccurMonth
----- ----------
20 2009-02-01
30 2010-06-01
30 2010-07-01
The other solutions posted on this site are similar, but:
1) don't include an ID column,
2) don't use the start date/end dates in the data or
3) use cursors, which are forbidden in my environment.

Answer 1

Try this:
;WITH
MonthRange AS
(
SELECT ID_No,
MinMonth = MIN(OccurMonth),
MaxMonth = MAX(OccurMonth)
FROM #InputTable
GROUP BY ID_No
),
AllMonths AS
(
SELECT ID_No,
OccurMonth = MinMonth
FROM MonthRange
UNION ALL
SELECT a.ID_No,
DATEADD(MONTH, 1, a.OccurMonth)
FROM AllMonths a
INNER JOIN MonthRange r ON a.ID_No = r.ID_No
WHERE a.OccurMonth < r.MaxMonth
)
SELECT a.*
FROM AllMonths a
LEFT JOIN #InputTable i ON a.ID_No = i.ID_No
AND a.OccurMonth = i.OccurMonth
WHERE i.ID_No IS NULL
OPTION (MAXRECURSION 0)
AllMonths is a recursive CTE that lists out all months between the min and max month for each ID_no. Then it's only a simple LEFT JOIN to find what month is missing in between.