Cannot increment values in a T-SQL CTE - sql-server

Question

I have a case where I need to write a CTE ( at least this seems like the best approach) . I have almost everything I need in place but one last issue. I am using a CTE to generate many millions of a records and then I will insert them into a table. The data itself is almost irrelevant except for three columns. 2 date time columns and one character column.
The idea behind the CTE is this. I want one datetime field called Start and one int field called DataValue. I will have a variable which is the count of records I want to aim for and then another variable which is the number of times I want to repeat the datetime value. I don't think I need to explain the software this data represents but basically I need to have 16 rows where the Start value is the same and then after the 16th run I want to then add 15 minutes and then repeat. Effectively there will be events in 15 minute intervals and I will need X number of rows per 15 minute interval to represent those events.
This is my code
Declare #tot as int;
Declare #inter as int;
Set #tot = 26
Set #inter = 3;
WITH mycte(DataValue,start) AS
(
SELECT 1 DataValue, cast('01/01/2011 00:00:00' as datetime) as start
UNION all
if DataValue % #inter = 0
SELECT
DataValue + 1,
cast(DateAdd(minute,15,start) as datetime)
else
select
DataValue + ,
start
FROM mycte
WHERE DataValue + 1 <= #tot)
select
m.start,
m.start,
m.Datavalue%#inter
from mycte as m
option (maxrecursion 0);
I'll change the select statement into an insert statement once I get it working but the m.DataValue%#inter will make it repeat integer when inserting so the only thing I need is to figure out how to make the start be the same 16 times in a row and then increment
It seems that I cannot have an IF statement in the CTE but I am not sure how to accomplish that but what I was going to do was basically say if the DataValue%16 was 0 then increase the value of start.
In the end I should hopefully have something like this where in this case I only repeat it 4 times
+-----------+-------------------+
| DateValue | start |
+-----------+-------------------+
| 1 | 01/01/01 00:00:00 |
| 2 | 01/01/01 00:00:00 |
| 3 | 01/01/01 00:00:00 |
| 4 | 01/01/01 00:00:00 |
| 5 | 01/01/01 00:15:00 |
| 6 | 01/01/01 00:15:00 |
| 7 | 01/01/01 00:15:00 |
| 8 | 01/01/01 00:15:00 |
Is there another way to accomplish this without conditional statements?

Answer 1

You can use case when as below:
Declare #tot as int;
Declare #inter as int;
Set #tot = 26
Set #inter = 3;
WITH mycte(DataValue,start) AS
(
SELECT 1 DataValue, cast('01/01/2011 00:00:00' as datetime) as start
UNION all
SELECT DataValue+1 [Datavalue],
case when (DataValue % #inter) = 0 then cast(DateAdd(minute,15,start) as datetime) else [start] end [start]
FROM mycte
WHERE (DataValue + 1) <= #tot)
select
m.DataValue,
m.[start]
from mycte as m
option (maxrecursion 0);
This will give the below result
DataValue Start
========= =============
1 2011-01-01 00:00:00.000
2 2011-01-01 00:00:00.000
3 2011-01-01 00:00:00.000
4 2011-01-01 00:15:00.000
5 2011-01-01 00:15:00.000
6 2011-01-01 00:15:00.000
7 2011-01-01 00:30:00.000
8 2011-01-01 00:30:00.000
9 2011-01-01 00:30:00.000
10 2011-01-01 00:45:00.000
11 2011-01-01 00:45:00.000
12 2011-01-01 00:45:00.000
....
26 2011-01-01 02:00:00.000
And if you dont want to use case when you can use double recursive cte as below:-
WITH mycte(DataValue,start) AS
( --this recursive cte will generate the same record the number of #inter
SELECT 1 DataValue, cast('01/01/2011 00:00:00' as datetime) as start
UNION all
SELECT DataValue+1 [DataValue],[start]
FROM mycte
WHERE (DataValue + 1) <= #inter)
,Increments as (
-- this recursive cte will do the 15 additions
select * from mycte
union all
select DataValue+#inter [DataValue]
,DateAdd(minute,15,[start]) [start]
from Increments
WHERE (DataValue + 1) <= #tot
)
select
m.DataValue,
m.[start]
from Increments as m
order by DataValue
option (maxrecursion 0);
it will give the same results.

Answer 2

You can do this with a tally table and some basic math. I'm not sure if your total rows are #tot or should they be #tot * #inter. If so, you just need to change the TOP clause. If you need more rows, you just need to alter the tally table generation.
Declare #tot as int;
Declare #inter as int;
Set #tot = 26
Set #inter = 3;
WITH
E(n) AS(
SELECT n FROM (VALUES(0),(0),(0),(0),(0),(0),(0),(0),(0),(0))E(n)
),
E2(n) AS(
SELECT a.n FROM E a, E b
),
E4(n) AS(
SELECT a.n FROM E2 a, E2 b
),
cteTally(n) AS(
SELECT TOP( #tot) ROW_NUMBER() OVER(ORDER BY (SELECT NULL)) n
FROM E4
)
SELECT n, DATEADD( MI, 15* ((n-1)/#inter), '20110101')
FROM cteTally;