SQL Server 2019

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CREATE TABLE SOLUTION (PID INT, OID INT,  CID INT, GRP INT)
insert into SOLUTION values 
(1,1,0, 0), 
(1,2,0, 0), 
(1,3,1, 1), 
(1,4,1, 1), 
(1,5,1, 1), 
(1,6,0, 2), 
(1,7,0, 2), 

(2,1,0, 0), 
(2,2,0, 0), 
(2,3,1, 1), 
(2,4,1, 1), 
(2,5,0, 2), 
(2,6,1, 3), 
(2,7,1, 3), 
(2,8,0, 4), 

(3,1,1, 1), 
(3,2,1, 1), 
(3,3,1, 1), 
(3,4,1, 1), 
(3,5,0, 2), 
(3,6,1, 3), 
(3,7,1, 3), 
(3,8,0, 4), 
(3,9,0, 4)
24 rows affected

select * from solution


PID
OID
CID
GRP


1
1
0
0

1
2
0
0

1
3
1
1

1
4
1
1

1
5
1
1

1
6
0
2

1
7
0
2

2
1
0
0

2
2
0
0

2
3
1
1

2
4
1
1

2
5
0
2

2
6
1
3

2
7
1
3

2
8
0
4

3
1
1
1

3
2
1
1

3
3
1
1

3
4
1
1

3
5
0
2

3
6
1
3

3
7
1
3

3
8
0
4

3
9
0
4


select s.*,
       sum(case when prev_cid = cid then 0 else 1 end) over (partition by pid order by oid) as grp
from (select s.*,
             lag(cid) over (partition by pid order by oid) as prev_cid
      from solution s
     ) s


PID
OID
CID
GRP
prev_cid
grp


1
1
0
0
null
1

1
2
0
0
0
1

1
3
1
1
0
2

1
4
1
1
1
2

1
5
1
1
1
2

1
6
0
2
1
3

1
7
0
2
0
3

2
1
0
0
null
1

2
2
0
0
0
1

2
3
1
1
0
2

2
4
1
1
1
2

2
5
0
2
1
3

2
6
1
3
0
4

2
7
1
3
1
4

2
8
0
4
1
5

3
1
1
1
null
1

3
2
1
1
1
1

3
3
1
1
1
1

3
4
1
1
1
1

3
5
0
2
1
2

3
6
1
3
0
3

3
7
1
3
1
3

3
8
0
4
1
4

3
9
0
4
0
4


with toupdate as (
      select s.*,
             sum(case when prev_cid = cid then 0 else 1 end) over (partition by pid order by oid) as new_grp
      from (select s.*,
                   lag(cid) over (partition by pid order by oid) as prev_cid
            from solution s
           ) s
     )
update toupdate
     set grp = new_grp
24 rows affected

PID	OID	CID	GRP
1	1	0	0
1	2	0	0
1	3	1	1
1	4	1	1
1	5	1	1
1	6	0	2
1	7	0	2
2	1	0	0
2	2	0	0
2	3	1	1
2	4	1	1
2	5	0	2
2	6	1	3
2	7	1	3
2	8	0	4
3	1	1	1
3	2	1	1
3	3	1	1
3	4	1	1
3	5	0	2
3	6	1	3
3	7	1	3
3	8	0	4
3	9	0	4

PID	OID	CID	GRP	prev_cid	grp
1	1	0	0	null	1
1	2	0	0	0	1
1	3	1	1	0	2
1	4	1	1	1	2
1	5	1	1	1	2
1	6	0	2	1	3
1	7	0	2	0	3
2	1	0	0	null	1
2	2	0	0	0	1
2	3	1	1	0	2
2	4	1	1	1	2
2	5	0	2	1	3
2	6	1	3	0	4
2	7	1	3	1	4
2	8	0	4	1	5
3	1	1	1	null	1
3	2	1	1	1	1
3	3	1	1	1	1
3	4	1	1	1	1
3	5	0	2	1	2
3	6	1	3	0	3
3	7	1	3	1	3
3	8	0	4	1	4
3	9	0	4	0	4

PID	OID	CID	GRP
1	1	0	0
1	2	0	0
1	3	1	1
1	4	1	1
1	5	1	1
1	6	0	2
1	7	0	2
2	1	0	0
2	2	0	0
2	3	1	1
2	4	1	1
2	5	0	2
2	6	1	3
2	7	1	3
2	8	0	4
3	1	1	1
3	2	1	1
3	3	1	1
3	4	1	1
3	5	0	2
3	6	1	3
3	7	1	3
3	8	0	4
3	9	0	4

PID	OID	CID	GRP
1	1	0	0
1	2	0	0
1	3	1	1
1	4	1	1
1	5	1	1
1	6	0	2
1	7	0	2
2	1	0	0
2	2	0	0
2	3	1	1
2	4	1	1
2	5	0	2
2	6	1	3
2	7	1	3
2	8	0	4
3	1	1	1
3	2	1	1
3	3	1	1
3	4	1	1
3	5	0	2
3	6	1	3
3	7	1	3
3	8	0	4
3	9	0	4