SQL Server 2017

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declare @t table (id int identity ,Element nvarchar(5), DateBegin datetime, DateEnd datetime)

 insert into @t
 (Element,DateBegin,DateEnd)
 values
 ('A', '2019-12-12 05:00:00', '2019-12-12 05:05:00'),
 ('A', '2019-12-12 05:02:00', '2019-12-12 05:07:00'),
 ('A', '2019-12-12 05:03:00', '2019-12-12 05:09:00'),
 ('A', '2019-12-12 05:11:00', '2019-12-12 05:15:00')
 ,('B', '2019-12-12 05:10:00', '2019-12-12 05:18:00')
 ,('B', '2019-12-12 05:17:00', '2019-12-12 05:19:00')
 ,('B', '2019-12-12 05:27:00', '2019-12-12 05:29:00')
 ,('C', '2019-12-12 04:24:00', '2019-12-12 04:26:00')
 ,('C', '2019-12-12 05:00:00', '2019-12-12 05:05:00')
 ,('C', '2019-12-12 05:01:00', '2019-12-12 05:05:00')
 ,('C', '2019-12-12 05:02:00', '2019-12-12 05:05:00')
 ,('C', '2019-12-12 05:03:00', '2019-12-12 05:05:00')
 ,('C', '2019-12-12 05:04:00', '2019-12-12 05:08:00')
 ,('C', '2019-12-12 05:04:00', '2019-12-12 05:07:00')
 ,('C', '2019-12-12 05:04:00', '2019-12-12 05:06:00')
 ,('C', '2019-12-12 05:14:00', '2019-12-12 05:16:00')
 ,('C', '2019-12-12 05:24:00', '2019-12-12 05:26:00')
 ,('C', '2019-12-12 05:25:00', '2019-12-12 05:27:00')

 ,('D', '2019-12-12 04:24:00', '2019-12-12 04:26:00')
 ,('D', '2019-12-12 05:00:00', '2019-12-12 05:05:00')
 ,('D', '2019-12-12 05:01:00', '2019-12-12 05:05:00')
 ,('D', '2019-12-12 05:02:00', '2019-12-12 05:05:00')
 ,('D', '2019-12-12 05:03:00', '2019-12-12 05:05:00')
 ,('D', '2019-12-12 05:04:00', '2019-12-12 05:08:00')
 ,('D', '2019-12-12 05:04:00', '2019-12-12 05:07:00')
 ,('D', '2019-12-12 05:04:00', '2019-12-12 05:06:00')
 ,('D', '2019-12-12 05:14:00', '2019-12-12 05:16:00')
 ,('D', '2019-12-12 05:24:00', '2019-12-12 05:26:00')
 ,('D', '2019-12-12 05:25:00', '2019-12-12 05:27:00') 
 ,('D', '1753-12-12 05:00:00', '2050-12-12 05:05:00');

with DatesСollapsed as
(select a.Element, 
        /*group by version*/        
        /*min(a.DateBegin) as DateStart*/
        min(a.DateBegin) 
         over(partition by a.Element, a.CoveringDateEnd) as DateStart,
        a.CoveringDateEnd as DateEnd
   from (select t.Element, t.DateBegin, t.DateEnd,
                max(t.DateEnd)
                 over(partition by t.Element order by t.DateBegin) as CoveringDateEnd
           from @t as t) as a
  /*group by a.Element, a.CoveringDateEnd*/)
  
, DatesGroupMarked as
(select b.Element, b.DateStart, b.DateEnd, 
        sum(b.CrossingDateStatus)
         over(partition by b.Element order by b.DateStart) as CrossingGroup
   from (select c.Element, c.DateStart, c.DateEnd,
                iif(lag(c.DateEnd, 1, c.DateStart)
                     over(partition by c.Element order by c.DateStart) >= c.DateStart, 0, 1) as CrossingDateStatus 
           from DatesСollapsed as c) as b)
           
, DatesFinal as
(select g.Element,
        min(g.DateStart) as DateStart,
        max(g.DateEnd) as DateEnd
   from DatesGroupMarked as g
  group by g.Element, g.CrossingGroup)
  
select f.Element, f.DateStart, f.DateEnd
  from DatesFinal as f
  
 order by f.Element, f.DateStart
  

  


Element
DateStart
DateEnd


A
12/12/2019 05:00:00
12/12/2019 05:09:00

A
12/12/2019 05:11:00
12/12/2019 05:15:00

B
12/12/2019 05:10:00
12/12/2019 05:19:00

B
12/12/2019 05:27:00
12/12/2019 05:29:00

C
12/12/2019 04:24:00
12/12/2019 04:26:00

C
12/12/2019 05:00:00
12/12/2019 05:08:00

C
12/12/2019 05:14:00
12/12/2019 05:16:00

C
12/12/2019 05:24:00
12/12/2019 05:27:00

D
12/12/1753 05:00:00
12/12/2050 05:05:00


declare @t table (Element nvarchar(5), DTS datetime, DTE datetime)

 insert into @t
 (Element,DTS,DTE)
 values ('A', '2019-12-12 05:00:00', '2019-12-12 05:05:00'),
 ('A', '2019-12-12 05:02:00', '2019-12-12 05:07:00'),
 ('A', '2019-12-12 05:03:00', '2019-12-12 05:09:00'),
 ('A', '2019-12-12 05:11:00', '2019-12-12 05:15:00')
 ,('B', '2019-12-12 05:10:00', '2019-12-12 05:18:00')
 ,('B', '2019-12-12 05:17:00', '2019-12-12 05:19:00')
 ,('B', '2019-12-12 05:27:00', '2019-12-12 05:29:00')
 ,('C', '2019-12-12 04:24:00', '2019-12-12 04:26:00')
 ,('C', '2019-12-12 05:00:00', '2019-12-12 05:05:00')
 ,('C', '2019-12-12 05:01:00', '2019-12-12 05:05:00')
 ,('C', '2019-12-12 05:02:00', '2019-12-12 05:05:00')
 ,('C', '2019-12-12 05:03:00', '2019-12-12 05:05:00')
 ,('C', '2019-12-12 05:04:00', '2019-12-12 05:08:00')
 ,('C', '2019-12-12 05:04:00', '2019-12-12 05:07:00')
 ,('C', '2019-12-12 05:04:00', '2019-12-12 05:06:00')
 ,('C', '2019-12-12 05:14:00', '2019-12-12 05:16:00')
 ,('C', '2019-12-12 05:24:00', '2019-12-12 05:26:00')
 ,('C', '2019-12-12 05:25:00', '2019-12-12 05:27:00')
 
 ,('D', '2019-12-12 04:24:00', '2019-12-12 04:26:00')
 ,('D', '2019-12-12 05:00:00', '2019-12-12 05:05:00')
 ,('D', '2019-12-12 05:01:00', '2019-12-12 05:05:00')
 ,('D', '2019-12-12 05:02:00', '2019-12-12 05:05:00')
 ,('D', '2019-12-12 05:03:00', '2019-12-12 05:05:00')
 ,('D', '2019-12-12 05:04:00', '2019-12-12 05:08:00')
 ,('D', '2019-12-12 05:04:00', '2019-12-12 05:07:00')
 ,('D', '2019-12-12 05:04:00', '2019-12-12 05:06:00')
 ,('D', '2019-12-12 05:14:00', '2019-12-12 05:16:00')
 ,('D', '2019-12-12 05:24:00', '2019-12-12 05:26:00')
 ,('D', '2019-12-12 05:25:00', '2019-12-12 05:27:00') 
 ,('D', '1753-12-12 05:00:00', '2050-12-12 05:05:00')
 
 
 
 ;with a as(
 select*
 ,ROW_NUMBER() over(partition by Element order by DTS) n
 from @t
 )
 select Element,MIN(DTS) DTS,MAX(DTE) DTE
 from(
   select Element,DTS,DTE,num
 from(
 select a.Element,a.DTS,a.DTE,
 ROW_NUMBER() over(partition by a.Element order by a.DTS) m,
  case when  a.DTE < a1.DTS then 1 else 0 end num
 from a
  join a a1 on a1.n - a.n = 1
  ) c
  where m=1
 union 
 select Element,DTS,DTE,max(num) num
 from(
 select a1.Element,a1.DTS,a1.DTE,
 ROW_NUMBER() over(partition by a.Element order by a.DTS) m,
  case when  a.DTE < a1.DTS then 1 else 0 end num
 from a
  join a a1 on a1.n - a.n = 1
  ) c
  where m>1
  group by Element,DTS,DTE
  
 ) b
 group by Element,num
 order by Element


Element
DTS
DTE


A
12/12/2019 05:00:00
12/12/2019 05:05:00

A
12/12/2019 05:03:00
12/12/2019 05:15:00

B
12/12/2019 05:10:00
12/12/2019 05:18:00

B
12/12/2019 05:17:00
12/12/2019 05:29:00

C
12/12/2019 05:02:00
12/12/2019 05:08:00

C
12/12/2019 04:24:00
12/12/2019 05:27:00

D
12/12/1753 05:00:00
12/12/2050 05:05:00

D
12/12/2019 05:00:00
12/12/2019 05:26:00


declare @t table (id int identity ,Element nvarchar(5), DateBegin datetime, DateEnd datetime)

 insert into @t
 (Element,DateBegin,DateEnd)
 values
 ('A', '2019-12-12 05:00:00', '2019-12-12 05:05:00'),
 ('A', '2019-12-12 05:02:00', '2019-12-12 05:07:00'),
 ('A', '2019-12-12 05:03:00', '2019-12-12 05:09:00'),
 ('A', '2019-12-12 05:11:00', '2019-12-12 05:15:00')
 ,('B', '2019-12-12 05:10:00', '2019-12-12 05:18:00')
 ,('B', '2019-12-12 05:17:00', '2019-12-12 05:19:00')
 ,('B', '2019-12-12 05:27:00', '2019-12-12 05:29:00')
 ,('C', '2019-12-12 04:24:00', '2019-12-12 04:26:00')
 ,('C', '2019-12-12 05:00:00', '2019-12-12 05:05:00')
 ,('C', '2019-12-12 05:01:00', '2019-12-12 05:05:00')
 ,('C', '2019-12-12 05:02:00', '2019-12-12 05:05:00')
 ,('C', '2019-12-12 05:03:00', '2019-12-12 05:05:00')
 ,('C', '2019-12-12 05:04:00', '2019-12-12 05:08:00')
 ,('C', '2019-12-12 05:04:00', '2019-12-12 05:07:00')
 ,('C', '2019-12-12 05:04:00', '2019-12-12 05:06:00')
 ,('C', '2019-12-12 05:14:00', '2019-12-12 05:16:00')
 ,('C', '2019-12-12 05:24:00', '2019-12-12 05:26:00')
 ,('C', '2019-12-12 05:25:00', '2019-12-12 05:27:00')
 
 ,('D', '2019-12-12 04:24:00', '2019-12-12 04:26:00')
 ,('D', '2019-12-12 05:00:00', '2019-12-12 05:05:00')
 ,('D', '2019-12-12 05:01:00', '2019-12-12 05:05:00')
 ,('D', '2019-12-12 05:02:00', '2019-12-12 05:05:00')
 ,('D', '2019-12-12 05:03:00', '2019-12-12 05:05:00')
 ,('D', '2019-12-12 05:04:00', '2019-12-12 05:08:00')
 ,('D', '2019-12-12 05:04:00', '2019-12-12 05:07:00')
 ,('D', '2019-12-12 05:04:00', '2019-12-12 05:06:00')
 ,('D', '2019-12-12 05:14:00', '2019-12-12 05:16:00')
 ,('D', '2019-12-12 05:24:00', '2019-12-12 05:26:00')
 ,('D', '2019-12-12 05:25:00', '2019-12-12 05:27:00') 
 ,('D', '1753-12-12 05:00:00', '2050-12-12 05:05:00')
 
;WITH CTE AS
(
  SELECT
    *,
    LAG(DateBegin)  OVER (PARTITION BY Element ORDER BY DateBegin, DateEnd) AS PrevBegin,
    LAG(DateEnd)    OVER (PARTITION BY Element ORDER BY DateBegin, DateEnd) AS PrevEnd   
  FROM @t

),
Groups AS
(
  SELECT *, SUM(CASE WHEN (PrevBegin <= DateEnd AND PrevEnd >= DateBegin) THEN 1 ELSE 0 END) OVER (PARTITION BY Element ORDER BY DateBegin, DateEnd) AS GRP
  FROM CTE
),
FinalGroups AS
(
  SELECT *, ROW_NUMBER() OVER (PARTITION BY Element ORDER BY DateBegin, DateEnd) - GRP AS FinalGroup
  FROM Groups
)
SELECT Element, MIN(DateBegin) AS DateBegin, MAX(DateEnd) AS DateEnd
FROM FinalGroups
GROUP BY Element, FinalGroup
ORDER BY 1, 2
 


Element
DateBegin
DateEnd


A
12/12/2019 05:00:00
12/12/2019 05:09:00

A
12/12/2019 05:11:00
12/12/2019 05:15:00

B
12/12/2019 05:10:00
12/12/2019 05:19:00

B
12/12/2019 05:27:00
12/12/2019 05:29:00

C
12/12/2019 04:24:00
12/12/2019 04:26:00

C
12/12/2019 05:00:00
12/12/2019 05:08:00

C
12/12/2019 05:14:00
12/12/2019 05:16:00

C
12/12/2019 05:24:00
12/12/2019 05:27:00

D
12/12/1753 05:00:00
12/12/2050 05:05:00

D
12/12/2019 05:00:00
12/12/2019 05:08:00

D
12/12/2019 05:14:00
12/12/2019 05:16:00

D
12/12/2019 05:24:00
12/12/2019 05:27:00
Element	DateStart	DateEnd
A	12/12/2019 05:00:00	12/12/2019 05:09:00
A	12/12/2019 05:11:00	12/12/2019 05:15:00
B	12/12/2019 05:10:00	12/12/2019 05:19:00
B	12/12/2019 05:27:00	12/12/2019 05:29:00
C	12/12/2019 04:24:00	12/12/2019 04:26:00
C	12/12/2019 05:00:00	12/12/2019 05:08:00
C	12/12/2019 05:14:00	12/12/2019 05:16:00
C	12/12/2019 05:24:00	12/12/2019 05:27:00
D	12/12/1753 05:00:00	12/12/2050 05:05:00
Element	DTS	DTE
A	12/12/2019 05:00:00	12/12/2019 05:05:00
A	12/12/2019 05:03:00	12/12/2019 05:15:00
B	12/12/2019 05:10:00	12/12/2019 05:18:00
B	12/12/2019 05:17:00	12/12/2019 05:29:00
C	12/12/2019 05:02:00	12/12/2019 05:08:00
C	12/12/2019 04:24:00	12/12/2019 05:27:00
D	12/12/1753 05:00:00	12/12/2050 05:05:00
D	12/12/2019 05:00:00	12/12/2019 05:26:00