How do you group by any time based interval?

Question

In SQL SERVER How do you group by any time based interval?

To save someone time I have come up with this solution, For me it works very well. You can generate any ti

Answer 1

I think you are over complicating thins.
You can use GROUP BY (DATEDIFF(MINUTE, '2017-01-01', TheDateTime) / 30 for grouping by every 30 minutes. Of course, the date I've chosen is a just a random date. You can choose, if you want, the first (or last) date in your sample data.
And you can also use this technique to get every interval of any time part - just change the keyword MINUTE to any date part you want to use, and the intreval 30 to any interval you want.

Consider the following sample data:

;WITH CTE AS 
(
    SELECT CAST('2017-01-01T00:00:00' as datetime) As TheDateTime, 0 as rn
    UNION ALL
    SELECT DATEADD(MINUTE, 1, TheDateTime), rn + 1
    FROM CTE
    WHERE rn < 60
)

SELECT TheDateTime, rn INTO #T
FROM CTE
OPTION(MAXRECURSION 0)

#T now contains the following data:

TheDateTime                 rn
2017-01-01 00:00:00.000     0
2017-01-01 00:01:00.000     1
2017-01-01 00:02:00.000     2
2017-01-01 00:03:00.000     3
...
2017-01-01 00:59:00.000     59
2017-01-01 01:00:00.000     60

To get the maximum rn grouped by 30 minutes you just need this:

SELECT DATEDIFF(MINUTE, '2017-01-01', TheDateTime) / 30, MAX(rn)
FROM #T
GROUP BY DATEDIFF(MINUTE, '2017-01-01', TheDateTime) / 30

Results:

interval    max_rn
0           29
1           59
2           60