insert into OREN_TEMP(TS)

values

('2019-10-25 06:20:07.000'),

('2019-10-25 06:20:15.000'),

('2019-10-25 06:20:19.000'),

('2019-10-25 06:20:26.000'),

('2019-10-25 06:20:26.000'),

('2019-10-25 06:20:34.000'),

('2019-10-25 06:20:42.000'),

('2019-10-25 06:20:51.000'),

('2019-10-25 06:20:59.000'),

('2019-10-25 06:21:07.000'),

('2019-10-25 06:21:15.000'),

('2019-10-25 06:21:19.000'),

('2019-10-25 06:21:26.000')

select * from OREN_TEMP

select top (1) ot.*

from oren_temp ot

order by ts asc

),

cte as (

select ts, 1 as lev

from first_row

union all

select ot.ts, lev + 1

from oren_temp ot join

cte

on ot.ts >= dateadd(second, 20, cte.ts)

)

select lev, min(ts)

from cte

group by lev;

select top (1) ot.*

from oren_temp ot

order by ts asc

),

cte as (

select ts, 1 as lev, convert(int, 1) as seqnum

from first_row

union all

select ot.ts, lev + 1, convert(int, row_number() over (partition by lev order by ot.ts)) as seqnum

from oren_temp ot join

cte

on ot.ts >= dateadd(second, 20, cte.ts)

where seqnum = 1

)

select lev, ts, seqnum

from cte

where seqnum = 1