How to build a recursive table in inline-table-valued function (iTVF)? - sql

Question

I have four parameters to be accepted by the function:
#FromDate DATE, #ToDate DATE, #DataInterval INT, #RangeInterval INT
The result set is obtained using a CTE:
;WITH Dates_CTE (FromDt, ToDt) AS
(
SELECT
DATEADD(D,-#RangeInterval,#FromDate) AS [FromDt],
#FromDate AS [ToDt]
UNION ALL
SELECT
DATEADD(D,#DataInterval,D.FromDt) AS [FromDt],
DATEADD(D,#DataInterval,D.ToDt) AS [ToDt]
FROM Dates_CTE D
WHERE D.ToDt <= #ToDate
)
But using a CTE makes it a multi-table-valued function and it becomes a performance-killer.
Is there another way to achieve this in an inline function?
The example of the desired result with the input #FromDate = '20180701', #ToDate = '20180901', #DataInterval = 5, #RangeInterval = 30 is:
+------------+------------+
| FromDate | ToDate |
+------------+------------+
| 2018-06-01 | 2018-07-01 |
| 2018-06-06 | 2018-07-06 |
| 2018-06-11 | 2018-07-11 |
| 2018-06-16 | 2018-07-16 |
| 2018-06-21 | 2018-07-21 |
| 2018-06-26 | 2018-07-26 |
| 2018-07-01 | 2018-07-31 |
| 2018-07-06 | 2018-08-05 |
| 2018-07-11 | 2018-08-10 |
| 2018-07-16 | 2018-08-15 |
| 2018-07-21 | 2018-08-20 |
| 2018-07-26 | 2018-08-25 |
| 2018-07-31 | 2018-08-30 |
| 2018-08-05 | 2018-09-04 |
+------------+------------+
How can we achieve this result in an iTVF? Thanks in advance.

Answer 1

Really you need no recursion. Use a table of numbers. Here the table of numbers is generated on the fly it can be persisted in the db for better perfomance.
DECLARE #FromDate DATE, #ToDate DATE, #DataInterval INT, #RangeInterval INT;
SELECT #FromDate = '20180701', #ToDate = '20180901', #DataInterval = 5, #RangeInterval = 30;
-- table of 1000 numbers starting 0
with t0(n) as (
select n
from (
values (1),(2),(3),(4),(5),(6),(7),(8),(9),(10)
) t(n)
),nmbs as(
select row_number() over(order by t1.n) - 1 n
from t0 t1, t0 t2, t0 t3
)
select
DATEADD(D, #DataInterval*n - #RangeInterval, #FromDate) FromDate
,DATEADD(D, #DataInterval*n, #FromDate) ToDate
from nmbs
where DATEADD(D, #DataInterval*n , #FromDate) <= #ToDate;
You may need to adjust where conditions per your requierments.
Demo with the persisted table of numbers (aka tally table).

Answer 2

You can use a tally table inside your inline table-value function.
CREATE TABLE Numbers (N INT PRIMARY KEY NOT NULL);
INSERT INTO Numbers
SELECT ROW_NUMBER() OVER(ORDER BY (SELECT NULL)) -1 N
FROM
(
VALUES (NULL), (NULL), (NULL), (NULL), (NULL)
) T1(V) CROSS JOIN
(
VALUES (NULL), (NULL), (NULL), (NULL), (NULL)
) T2(VV) CROSS JOIN
(
VALUES (NULL), (NULL), (NULL), (NULL), (NULL) --Add Values as needed
) T3(VVV);
Then create your function as
CREATE FUNCTION dbo.MyFunc
(
#FromDate DATE,
#ToDate DATE,
#DataInterval INT,
#RangeInterval INT
)
RETURNS TABLE
RETURN
SELECT DATEADD(Day, (#DataInterval * N) - #RangeInterval, #FromDate) FromDate,
DATEADD(Day, #DataInterval * N, #FromDate) ToDate
FROM Numbers
WHERE DATEADD(Day, #DataInterval * N, #FromDate) <= #ToDate;
And finally, use it as
SELECT *
FROM dbo.MyFunc ('20180701', '20180901', 5, 30);
Online Demo

Answer 3

you can use while :
declare #FromDate DATE = '20180701', #ToDate DATE= '20180901', #DataInterval INT= 5, #RangeInterval INT= 30,#date date ,#r int =0
declare #table table (d1 date, d2 date)
set #date= #FromDate
while (#date <#ToDate )
begin
insert into #table
select dateadd(d,#r,#FromDate ),DATEADD(D,-#RangeInterval+#r,#FromDate)
set #r=#r+#DataInterval
set #date = dateadd(d,#r,#FromDate )
end
select * from #table