MSSQL: Generate Dates Between 2 Dates With Month Breaks - sql-server

Question

Struggling a bit with this...
I have a table with the following columns:
Type varchar
StartDate datetime
EndDate datetime
Interval int
What I want is a results table with the type column and all the dates between the start date and end date, using the interval as month breaks between them.
For instance if the only row in my table is:
'Test', '2017-01-01', '2019-01-01', 6
I want a results table that has 5 rows, with 'Test' as the Type on every row, and a date column that goes from:
'2017-01-01',
'2017-07-01',
'2018-01-01',
etc.
I've created a Calendar table and even a DateRange function where I pass in a start date, end date and month interval which returns me all the dates I'd want, but since it's a table-valued function I don't seem to be able to call it with data from another table.
How do I do this?
Thanks.

Answer 1

I'll often use a TVF to create dynamic Date/Time Ranges. A tally/calendar table will do the trick as well, but the UDF offers some additional functionality. For example, you supply the Range, DatePart and Increment
Declare #YourTable table ([Type] varchar(25),StartDate date,EndDate date,Interval int)
Insert Into #YourTable values
('Test','2017-01-01','2019-01-01', 6)
Select A.[Type]
,B.*
From #YourTable A
Cross Apply [dbo].[udf-Range-Date](A.StartDate,A.EndDate,'MM', A.Interval) B
Returns
Type RetSeq RetVal
Test 1 2017-01-01
Test 2 2017-07-01
Test 3 2018-01-01
Test 4 2018-07-01
Test 5 2019-01-01
The UDF if Interested
CREATE FUNCTION [dbo].[udf-Range-Date] (#R1 datetime,#R2 datetime,#Part varchar(10),#Incr int)
Returns Table
Return (
with cte0(M) As (Select 1+Case #Part When 'YY' then DateDiff(YY,#R1,#R2)/#Incr When 'QQ' then DateDiff(QQ,#R1,#R2)/#Incr When 'MM' then DateDiff(MM,#R1,#R2)/#Incr When 'WK' then DateDiff(WK,#R1,#R2)/#Incr When 'DD' then DateDiff(DD,#R1,#R2)/#Incr When 'HH' then DateDiff(HH,#R1,#R2)/#Incr When 'MI' then DateDiff(MI,#R1,#R2)/#Incr When 'SS' then DateDiff(SS,#R1,#R2)/#Incr End),
cte1(N) As (Select 1 From (Values(1),(1),(1),(1),(1),(1),(1),(1),(1),(1)) N(N)),
cte2(N) As (Select Top (Select M from cte0) Row_Number() over (Order By (Select NULL)) From cte1 a, cte1 b, cte1 c, cte1 d, cte1 e, cte1 f, cte1 g, cte1 h ),
cte3(N,D) As (Select 0,#R1 Union All Select N,Case #Part When 'YY' then DateAdd(YY, N*#Incr, #R1) When 'QQ' then DateAdd(QQ, N*#Incr, #R1) When 'MM' then DateAdd(MM, N*#Incr, #R1) When 'WK' then DateAdd(WK, N*#Incr, #R1) When 'DD' then DateAdd(DD, N*#Incr, #R1) When 'HH' then DateAdd(HH, N*#Incr, #R1) When 'MI' then DateAdd(MI, N*#Incr, #R1) When 'SS' then DateAdd(SS, N*#Incr, #R1) End From cte2 )
Select RetSeq = N+1
,RetVal = D
From cte3,cte0
Where D<=#R2
)
/*
Max 100 million observations -- Date Parts YY QQ MM WK DD HH MI SS
Syntax:
Select * from [dbo].[udf-Range-Date]('2016-10-01','2020-10-01','YY',1)
Select * from [dbo].[udf-Range-Date]('2016-01-01','2017-01-01','MM',1)
*/