Question

I want to delete set of the rows from a table. I can decide which rows need to be deleted. I will delete the rows from table only if the count of rows is more than 5 (based on condition).

Consider this sample data

ID--Col1--Col2--
1   A      X
2   A      X
3   A      X
4   A      X
5   A      X
6   A      X
7   A      X
8   A      X
9   A      X
10   A      X
11   B      X
12   B      X
13   B      X
14   B      X
15   C      X
16   C      X
17   C      X
18   D      X
19   D      X

I want to delete 5 Rows of {*, A, X}, I need to keep 5 of them (no matter which one). I wont delete B, C & D since count of them is less then 5.

Like

delete from tableA
 --- I can decide on the rows to delete based on two conditions.
 where col1 = someCondition
   and col2 = someOtherCondition
   and rownum > 5 --- This dint work. I checked.

I think perhaps I need to programmaticaly. Any suggestions are greatly appreciated.

Answer 1

This will delete all rows for each unique combination of col1 and col2 other than the first five ordered by rowid

delete from my_table
where rowid in
  (
  select rowid
  from
    (
    select rowid,
           row_number() over (partition by col1, col2 order by rowid) rownumber
    from   my_table
    )
  where rownumber > 5
  )
/