SQL Server 2019

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create table tbl
(
 Id int identity(1,1)
 , Prod varchar(1)
 , Id2 int
)
insert into tbl values ('A', 11), ('A', 11), ('A', 11), ('B', 12), ('B', 12), ('A', 13), ('B', 14), ('D', 15)
8 rows affected

select *
    , case
        when row_number() over (partition by Id2 order by Id) = 1 then 0
        else 1
      end Flag
from tbl
order by Id


Id
Prod
Id2
Flag


1
A
11
0

2
A
11
1

3
A
11
1

4
B
12
0

5
B
12
1

6
A
13
0

7
B
14
0

8
D
15
0