How can I update the table with a single query for...

Question

I have a table with columns C1 and C2.
C1 C2
A1 null
A1 null
A1 null
A1 null
A2 null
A2 null
A2 null
A3 null
A4 null
A4 null
I want to update my table with a single query so that I would have data like
C1 C2
A1 1
A1 2
A1 3
A1 4
A2 1
A2 2
A2 3
A3 1
A4 1
A4 2
The updated column C2 has the values like serial no grouped on the column C1.

Answer 1

SQL> create table mytable
  2  ( c1 varchar2(2)
  3  , c2 number(2)
  4  )
  5  /
Tabel is aangemaakt.
SQL> insert into mytable (c1)
  2  select 'A1' from dual union all
  3  select 'A1' from dual union all
  4  select 'A1' from dual union all
  5  select 'A1' from dual union all
  6  select 'A2' from dual union all
  7  select 'A2' from dual union all
  8  select 'A2' from dual union all
  9  select 'A3' from dual union all
10  select 'A4' from dual union all
11  select 'A4' from dual
12  /
10 rijen zijn aangemaakt.
SQL> select * from mytable
  2  /
C1                                     C2
A1
A1
A1
A1
A2
A2
A2
A3
A4
A4
10 rijen zijn geselecteerd.
SQL> merge into mytable t1
  2  using (select c1
  3              , row_number() over (partition by c1 order by null) rn
  4              , rowid rid
  5           from mytable
  6        ) t2
  7     on (t1.rowid = t2.rid)
  8   when matched then
  9        update set c2 = rn
10   when not matched then
11        insert values (null,null)
12  /
10 rijen zijn samengevoegd.
SQL> select * from mytable
  2  /
C1                                     C2
A1                                      1
A1                                      2
A1                                      3
A1                                      4
A2                                      1
A2                                      2
A2                                      3
A3                                      1
A4                                      1
A4                                      2
10 rijen zijn geselecteerd.Regards,
Rob.