Sum of values each hour at half past (that hour)

Question

I need to aggregate the "sum" of values of a table with TS, Value columns of each half past hour (of 60 minutes), i.e. 00:30, 01:30, 02:30, etc

Sample data:

Val TS
1   2019-08-12 00:00:00.013
3   2019-08-12 00:10:00.013
2   2019-08-12 00:20:00.013
2   2019-08-12 00:30:00.013
0   2019-08-12 00:40:00.013
0   2019-08-12 00:50:00.013
1   2019-08-12 01:00:00.013
7   2019-08-12 01:10:00.013
0   2019-08-12 01:20:00.013
1   2019-08-12 01:30:00.013
2   2019-08-12 01:40:00.013
0   2019-08-12 01:50:00.013
2   2019-08-12 02:00:00.013
0   2019-08-12 02:10:00.013
0   2019-08-12 02:20:00.013
0   2019-08-12 02:30:00.013
1   2019-08-12 02:40:00.013
0   2019-08-12 02:50:00.013
4   2019-08-12 03:00:00.013
3   2019-08-12 03:20:00.013
1   2019-08-12 03:30:00.013

We should get this:

Val TS
10  2019-08-12 00:30:00
5   2019-08-12 01:30:00
8   2019-08-12 02:30:00

Can someone advise on this?

Thank you,

Answer 1

Given the data:

CREATE TABLE #Demo 
(
    Val integer NOT NULL, 
    TS datetime2(3) NOT NULL
);

INSERT #Demo 
    (Val, TS)
VALUES
(1, '2019-08-12 00:00:00.013'),
(3, '2019-08-12 00:10:00.013'),
(2, '2019-08-12 00:20:00.013'),
(2, '2019-08-12 00:30:00.013'),
(0, '2019-08-12 00:40:00.013'),
(0, '2019-08-12 00:50:00.013'),
(1, '2019-08-12 01:00:00.013'),
(7, '2019-08-12 01:10:00.013'),
(0, '2019-08-12 01:20:00.013'),
(1, '2019-08-12 01:30:00.013'),
(2, '2019-08-12 01:40:00.013'),
(0, '2019-08-12 01:50:00.013'),
(2, '2019-08-12 02:00:00.013'),
(0, '2019-08-12 02:10:00.013'),
(0, '2019-08-12 02:20:00.013'),
(0, '2019-08-12 02:30:00.013'),
(1, '2019-08-12 02:40:00.013'),
(0, '2019-08-12 02:50:00.013'),
(4, '2019-08-12 03:00:00.013'),
(3, '2019-08-12 03:20:00.013'),
(1, '2019-08-12 03:30:00.013');

One approach is:

• Calculate the number of minutes from a fixed date (with no time component)
• Add 30 minutes to each time to align half-hour slots to hours
• Round to the hour (divide then multiply minutes by 60 using integer math)
• Subtract the 30 minutes
• Add the minutes to the same fixed date

This is shown in the code below:

SELECT
    TS = CONVERT(char(19), Timeslot.TS, 120),
    Val = SUM(D.Val)
FROM #Demo AS D
CROSS JOIN (VALUES(CONVERT(datetime2(3), '20190101', 112))) AS Base(FixedDate)
CROSS APPLY(VALUES((DATEDIFF(MINUTE, Base.FixedDate, D.TS) + 30) / 60 * 60)) AS Slot(InMins)
CROSS APPLY(VALUES(DATEADD(MINUTE, Slot.InMins - 30, Base.FixedDate))) AS Timeslot(TS)
GROUP BY
    Timeslot.TS
ORDER BY
    Timeslot.TS;

Output:

╔═════════════════════╦═════╗
║         TS          ║ Val ║
╠═════════════════════╬═════╣
║ 2019-08-11 23:30:00 ║   6 ║
║ 2019-08-12 00:30:00 ║  10 ║
║ 2019-08-12 01:30:00 ║   5 ║
║ 2019-08-12 02:30:00 ║   8 ║
║ 2019-08-12 03:30:00 ║   1 ║
╚═════════════════════╩═════╝

db<>fiddle demo

This produces a couple of extra periods compared with the output shown in the question, but it nevertheless looks correct to me.

---

If you prefer the (somewhat slow) FORMAT function, the following is equivalent:

SELECT
    TS = Slot.TS,
    Val = SUM(D.Val)
FROM #Demo AS D
CROSS APPLY
(
    VALUES
    (
        -- Remove 30 minutes
        DATEADD(MINUTE, -30, 
            CONVERT(datetime2(3),
                FORMAT(
                    -- Add 30 minutes
                    DATEADD(MINUTE, 30, D.TS), 
                    -- Truncate to hour
                    N'yyyy-MM-dd HH:00:00', 
                    N'en-us'
                ), 120
            )
        )
    )
) AS Slot (TS)
GROUP BY
    Slot.TS
ORDER BY
    Slot.TS;