T-SQL list of years and months between two dates - tsql

Question

I have a table with a list of individuals that have a effective date and a termination date.
example Person 1, 20171201, 20180601
For each record, I need to output a list of years and months they were "active" between the two dates.
So the output would look like
Data Output
This is in SQL Server 2016
Any help would be appreciated!

Answer 1

Just because I did not see it offered. Here is yet another approach which uses an ad-hoc calendar table
Note the base date of 2000-01-01 and 10,000 days ... expand or contract if needed
Example
Declare #YourTable table (Person int,startdate date, enddate date)
Insert Into #YourTable values
(1,'20171201','20180601')
Select Distinct
A.Person
,ActiveYear = year(D)
,ActiveMonth = month(D)
From #YourTable A
Join (
Select Top 10000 D=DateAdd(DAY,-1+Row_Number() Over (Order By (Select Null)),'2000-01-01')
From master..spt_values n1,master..spt_values n2
) B on D between startdate and enddate
Returns
Person ActiveYear ActiveMonth
1 2017 12
1 2018 1
1 2018 2
1 2018 3
1 2018 4
1 2018 5
1 2018 6

Answer 2

Based on info you've provided, I did a little guessing. Perhaps a recursive CTE will help:
DECLARE #tab TABLE (Person INT, EffectiveDate DATE, TerminationDate DATE)
INSERT #tab VALUES
(1, '2017-12-01', '2018-05-31'),
(2, '2017-10-01', '2018-01-01'),
(3, '2018-02-01', '2018-12-01')
;WITH t AS (
SELECT Person, EffectiveDate AS Dt
FROM #tab
UNION ALL
SELECT Person, DATEADD(mm,1,Dt)
FROM t
WHERE t.Dt < (SELECT DATEADD(mm,-1,TerminationDate) FROM #tab tt WHERE tt.Person = t.Person)
)
SELECT *
FROM t
ORDER BY Dt
Then take the DATEPART()
SELECT t.Person
, t.Dt
, DATEPART(yyyy, t.Dt) ActiveYear
, DATEPART(mm, t.Dt) ActiveMonth
FROM t
ORDER BY Dt

Answer 3

Welcome to stackoverflow! For better help it's good to include DDL easily consumable sample data that we can use to quickly re-create what you are doing and provide a solution. Note this sample data:
DECLARE #yourtable TABLE(person VARCHAR(20), date1 DATE, date2 DATE)
INSERT #yourtable (person, date1, date2)
VALUES ('Person1','20171201', '20180601'), ('Person2','20171001', '20180101'),
('Person3','20180101', '20180301');
SELECT t.* FROM #yourtable AS t;
Returns:
person date1 date2
-------------------- ---------- ----------
Person1 2017-12-01 2018-06-01
Person2 2017-10-01 2018-01-01
Person3 2018-01-01 2018-03-01
(I added a couple rows). Here's my solution:
DECLARE #yourtable TABLE(person VARCHAR(20), date1 DATE, date2 DATE)
INSERT #yourtable (person, date1, date2)
VALUES ('Person1','20171201', '20180601'), ('Person2','20171001', '20180101'),
('Person3','20180101', '20180301');
SELECT
Person = t.person,
ActiveYear = YEAR(st.DT),
ActiveMonth = MONTH(st.Dt)
FROM #yourtable AS t
CROSS APPLY
(
SELECT TOP (DATEDIFF(MONTH,t.date1,t.date2)) ROW_NUMBER() OVER (ORDER BY (SELECT NULL))
FROM (VALUES(1),(1),(1),(1),(1),(1),(1),(1),(1),(1)) AS a(x)
CROSS JOIN (VALUES(1),(1),(1),(1),(1),(1),(1),(1),(1),(1)) AS b(x)
) AS iTally(N)
CROSS APPLY (VALUES(DATEADD(MONTH, iTally.N-1, t.date1))) AS st(Dt);
Which returns:
Person ActiveYear ActiveMonth
-------------------- ----------- -----------
Person1 2017 12
Person1 2018 1
Person1 2018 2
Person1 2018 3
Person1 2018 4
Person1 2018 5
Person2 2017 10
Person2 2017 11
Person2 2017 12
Person3 2018 1
Person3 2018 2
Let me know if you have questions.