SQL Server 2017

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create table ADates (Id int, SharedId int, TheDateTime datetime2(7));
insert into ADates values ( 1, 1, CAST('2019-01-01 01:01:00.00'AS datetime2(7)));
insert into ADates values ( 2, 1, CAST('2019-01-01 01:01:33.00'AS datetime2(7)));
insert into ADates values ( 3, 1, CAST('2019-01-01 01:02:00.00'AS datetime2(7)));
insert into ADates values ( 4, 1, CAST('2019-01-01 01:02:01.00'AS datetime2(7)));
insert into ADates values ( 5, 1, CAST('2019-01-01 01:02:04.00'AS datetime2(7)));
insert into ADates values ( 6, 1, CAST('2019-01-01 01:06:15.00'AS datetime2(7)));
insert into ADates values ( 7, 2, CAST('2019-01-01 01:06:00.00'AS datetime2(7)));
insert into ADates values ( 8, 2, CAST('2019-01-01 01:06:45.00'AS datetime2(7)));
insert into ADates values ( 9, 1, CAST('2019-01-01 01:02:31.00'AS datetime2(7)));
insert into ADates values (10, 2, CAST('2019-01-01 01:06:05.00'AS datetime2(7)));
insert into ADates values (11, 2, CAST('2019-01-01 01:06:46.00'AS datetime2(7)));
        
11 rows affected

WITH CteBase
AS
(
        SELECT  v.SharedId,
                v.TheDateTime,
                ROW_NUMBER() OVER(PARTITION BY v.SharedId ORDER BY v.TheDateTime) 
                       AS RowNum
        FROM    ADates v
),  CteRecursive
AS
(
        SELECT  crt.SharedId,
                crt.TheDateTime,
                crt.TheDateTime AS GroupStartDateTime,
                crt.RowNum,
                1 AS SharedIdRowNum
        FROM    CteBase crt
        WHERE   crt.RowNum = 1
        UNION ALL
        SELECT  crt.SharedId,
                crt.TheDateTime,
                CASE 
                    WHEN DATEDIFF(SECOND, prv.GroupStartDateTime, crt.TheDateTime) <= 30 
                    THEN prv.GroupStartDateTime 
                    ELSE crt.TheDateTime 
                END,
                crt.RowNum,
                CASE 
                    WHEN DATEDIFF(SECOND, prv.GroupStartDateTime, crt.TheDateTime) <= 30 
                    THEN prv.SharedIdRowNum + 1
                    ELSE 1
                END             
        FROM    CteBase crt
        INNER JOIN CteRecursive prv ON crt.SharedId = prv.SharedId 
        AND     crt.RowNum = prv.RowNum + 1
)
SELECT  r.SharedId,
        r.GroupStartDateTime
FROM    CteRecursive r
WHERE   r.SharedIdRowNum = 1
ORDER BY r.SharedId, r.GroupStartDateTime;


SharedId
GroupStartDateTime


1
01/01/2019 01:01:00

1
01/01/2019 01:01:33

1
01/01/2019 01:02:04

1
01/01/2019 01:06:15

2
01/01/2019 01:06:00

2
01/01/2019 01:06:45


WITH CteBase
AS
(
        SELECT  v.SharedId,
                v.TheDateTime,
                ROW_NUMBER() OVER(PARTITION BY v.SharedId ORDER BY v.TheDateTime) 
                       AS RowNum
        FROM    ADates v
),  CteRecursive
AS
(
        SELECT  crt.SharedId,
                crt.TheDateTime,
                crt.TheDateTime AS GroupStartDateTime,
                crt.RowNum,
                1 AS SharedIdRowNum
        FROM    CteBase crt
        WHERE   crt.RowNum = 1
        UNION ALL
        SELECT  crt.SharedId,
                crt.TheDateTime,
                CASE 
                    WHEN DATEDIFF(SECOND, prv.GroupStartDateTime, crt.TheDateTime) <= 30 
                    THEN prv.GroupStartDateTime 
                    ELSE crt.TheDateTime 
                END,
                crt.RowNum,
                CASE 
                    WHEN DATEDIFF(SECOND, prv.GroupStartDateTime, crt.TheDateTime) <= 30 
                    THEN prv.SharedIdRowNum + 1
                    ELSE 1
                END             
        FROM    CteBase crt
        INNER JOIN CteRecursive prv ON crt.SharedId = prv.SharedId 
        AND     crt.RowNum = prv.RowNum + 1
)
SELECT SharedId, Count(*) as [COUNT] FROM (
        SELECT  r.SharedId,
                r.GroupStartDateTime
        FROM    CteRecursive r
        WHERE   r.SharedIdRowNum = 1
) X
GROUP BY SharedId;


SharedId
COUNT


1
4

2
2
SharedId	GroupStartDateTime
1	01/01/2019 01:01:00
1	01/01/2019 01:01:33
1	01/01/2019 01:02:04
1	01/01/2019 01:06:15
2	01/01/2019 01:06:00
2	01/01/2019 01:06:45