select record after interval of at least 1 minute

Question

I have an application that logs data after around 1 second if the packet is healthy which means the logging is not guaranteed. Now the client wants to see the log data only with the gap of at least 1 minute. For example, this the sample schema and data

declare @mytable as table(ID int, tm DATETIME, Val int)

insert into @mytable values
(1,     convert(DATETIME, N'2018-12-24 17:45:25.000', 21), 1),
(2,     convert(DATETIME, N'2018-12-24 17:45:35.000', 21), 2),
(3,     convert(DATETIME, N'2018-12-24 17:45:55.000', 21), 1),
(4,     convert(DATETIME, N'2018-12-24 17:46:05.000', 21), 5),
(5,     convert(DATETIME, N'2018-12-24 17:47:25.000', 21), 2),
(6,     convert(DATETIME, N'2018-12-24 17:47:55.000', 21), 7),
(7,     convert(DATETIME, N'2018-12-24 17:48:25.000', 21), 9),
(8,     convert(DATETIME, N'2018-12-24 17:48:50.000', 21), 1),
(9,     convert(DATETIME, N'2018-12-24 17:49:25.000', 21), 1),
(10,    convert(DATETIME, N'2018-12-24 17:50:05.000', 21), 5),
(11,    convert(DATETIME, N'2018-12-24 17:50:50.000', 21), 4),
(12,    convert(DATETIME, N'2018-12-24 17:51:25.000', 21), 8),
(13,    convert(DATETIME, N'2018-12-24 17:55:25.000', 21), 4),
(14,    convert(DATETIME, N'2018-12-24 17:56:58.000', 21), 4),
(15,    convert(DATETIME, N'2018-12-24 17:58:15.000', 21), 5),
(16,    convert(DATETIME, N'2018-12-24 18:10:25.000', 21), 8);

The output should be

1,     convert(DATETIME, N'2018-12-24 17:45:25.000', 21), 1
5,     convert(DATETIME, N'2018-12-24 17:47:25.000', 21), 2
7,     convert(DATETIME, N'2018-12-24 17:48:25.000', 21), 9
9,     convert(DATETIME, N'2018-12-24 17:49:25.000', 21), 1
11,    convert(DATETIME, N'2018-12-24 17:50:50.000', 21), 4
13,    convert(DATETIME, N'2018-12-24 17:55:25.000', 21), 4
14,    convert(DATETIME, N'2018-12-24 17:56:58.000', 21), 4
15,    convert(DATETIME, N'2018-12-24 17:58:15.000', 21), 5
16,    convert(DATETIME, N'2018-12-24 18:10:25.000', 21), 8

Here, after a qualified entry, next entry to qualify is to have at least 1 minute gap. However, I have to log all the healthy entries as in some other procedure I'll have to return all records. So skipping during logging is not an option. Also, I know I can achieve it using a cursor but given the amount of data, this is not an acceptable solution.

Answer 1

Using recursive common table expression:

;WITH CTE (Id, tm, val)
AS
(
    SELECT TOP 1 *
    FROM @mytable m
    WHERE m.ID = 1

    UNION ALL

    SELECT
        p.Id,
        p.tm,
        p.val
    FROM
    (
        SELECT
            m.*, 
            ROW_NUMBER() OVER(ORDER BY c.Id) AS row_num
        FROM CTE c
        INNER JOIN @mytable m ON c.Id < m.ID AND DATEADD(MINUTE, 1, c.tm) <= m.tm
    ) AS p
    WHERE p.row_num = 1

)
SELECT *
FROM CTE c

Id          tm                      val
----------- ----------------------- -----------
1           2018-12-24 17:45:25.000 1
5           2018-12-24 17:47:25.000 2
7           2018-12-24 17:48:25.000 9
9           2018-12-24 17:49:25.000 1
11          2018-12-24 17:50:50.000 4
13          2018-12-24 17:55:25.000 4
14          2018-12-24 17:56:58.000 4
15          2018-12-24 17:58:15.000 5
16          2018-12-24 18:10:25.000 8

But, I'm not sure, this solution will work on big tables with many records. Maybe, you need some kind of post-processing after inserting in log table.