Deleting consecutive duplicates

Question

hi,
i have the below requirements:
1)my table consisits of below records:
id, code
1,A
1,A
2,B
1,A
i want to remove consecutive duplictaes and my o/p should be
1,A
2,B
1,A
2)second requirement is
id,code
1,A
2,A
3,B
4,A
i want to remove the duplicate based on code field alone/
My o/p should be
id,code
1,A
3,B
4,A
Please help me to achieve this.
Any ideas will be helpful
Thanks,
Pandeeswaran

Answer 1

>
1)my table consisits of below records:
id, code
1,A
1,A
2,B
1,A
i want to remove consecutive duplictaes and my o/p should be
1,A
2,B
1,A
Not possible. There is no row order in relational tables. Only ORDER BY guarantees row order.
2)second requirement is
id,code
1,A
2,A
3,B
4,A
i want to remove the duplicate based on code field alone/
My o/p should be
id,code
1,A
3,B
4,A
Here it is possible since ORDER BY id will produce right order:
SQL> select * from tbl
  2  order by id
  3  /
        ID C
         1 A
         2 A
         3 B
         4 A
SQL> delete tbl
  2    where rowid in (
  3                    select  rowid
  4                      from  (
  5                             select  rowid,
  6                                     case lag(code) over(order by id)
  7                                       when code then 0
  8                                       else 1
  9                                     end start_of_group
10                               from  tbl
11                            )
12                      where start_of_group = 0
13                   )
14  /
1 row deleted.
SQL> select * from tbl
  2  order by id
  3  /
        ID C
         1 A
         3 B
         4 A
SQL> SY.