SQL Server 2017

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CREATE TABLE T
	([No] int, [Time] datetime, [Temp] int, [Power] int)
;
	
INSERT INTO T
	([No], [Time], [Temp], [Power])
VALUES
	(1, '2019-11-04 00:00:00', 25, 1200),
	(2, '2019-11-04 00:01:10', 30, 1000),
	(3, '2019-11-04 00:02:20', 31, 680),
	(4, '2019-11-04 00:03:30', 34, 960),
	(5, '2019-11-04 00:04:40', 29, 800),
	(6, '2019-11-04 00:05:50', 31, 600),
	(7, '2019-11-04 00:07:00', 32, 400),
	(8, '2019-11-04 00:08:10', 33, 900),
	(9, '2019-11-04 00:09:20', 34, 1000),
	(10, '2019-11-04 00:10:30', 39, 200),
	(11, '2019-11-04 00:11:40', 24, 350)
;
11 rows affected

with cte as (
	select 
	 LAG(No, 1,0) OVER (ORDER BY No) AS PreviousNo,
	 null AS GroupId,
	 *
	from T
	where Temp > 30 
)
select * into #T from cte;
7 rows affected

select * from #T


PreviousNo
GroupId
No
Time
Temp
Power


0
null
3
04/11/2019 00:02:20
31
680

3
null
4
04/11/2019 00:03:30
34
960

4
null
6
04/11/2019 00:05:50
31
600

6
null
7
04/11/2019 00:07:00
32
400

7
null
8
04/11/2019 00:08:10
33
900

8
null
9
04/11/2019 00:09:20
34
1000

9
null
10
04/11/2019 00:10:30
39
200


DECLARE @tmp_no int,@groupId int = 1;

DECLARE MY_CURSOR CURSOR 
  LOCAL STATIC READ_ONLY FORWARD_ONLY
FOR 
SELECT No 
FROM #T

OPEN MY_CURSOR
FETCH NEXT FROM MY_CURSOR INTO @tmp_no
WHILE @@FETCH_STATUS = 0
BEGIN 
    if not (( select PreviousNo from #T where No = @tmp_no ) = @tmp_no - 1)  begin
       set @groupId = @groupId + 1;
    end
    update #T set groupId = @groupId where no = @tmp_no;
    FETCH NEXT FROM MY_CURSOR INTO @tmp_no
END
CLOSE MY_CURSOR
DEALLOCATE MY_CURSOR
7 rows affected

select * from #T


PreviousNo
GroupId
No
Time
Temp
Power


0
2
3
04/11/2019 00:02:20
31
680

3
2
4
04/11/2019 00:03:30
34
960

4
3
6
04/11/2019 00:05:50
31
600

6
3
7
04/11/2019 00:07:00
32
400

7
3
8
04/11/2019 00:08:10
33
900

8
3
9
04/11/2019 00:09:20
34
1000

9
3
10
04/11/2019 00:10:30
39
200


select 
   convert(varchar(3),min(no)) + ' to ' + convert(varchar(3),max(no)) as no_range
   ,avg(power) as avgpower
   ,min(Time) as mintime
   ,max(Time) as maxtime
   , datediff(minute,min(Time),max(Time)) timediff
from #T
group by groupid having datediff(minute,min(Time),max(Time)) > 3


no_range
avgpower
mintime
maxtime
timediff


6 to 10
620
04/11/2019 00:05:50
04/11/2019 00:10:30
5

PreviousNo	GroupId	No	Time	Temp	Power
0	null	3	04/11/2019 00:02:20	31	680
3	null	4	04/11/2019 00:03:30	34	960
4	null	6	04/11/2019 00:05:50	31	600
6	null	7	04/11/2019 00:07:00	32	400
7	null	8	04/11/2019 00:08:10	33	900
8	null	9	04/11/2019 00:09:20	34	1000
9	null	10	04/11/2019 00:10:30	39	200