Query on Views

Question

Hello everyone,
Can someone please explain me why cant we delete a row from a view that has some group function or group by clause or ROWNUM column or DISTINCT Keyword or any columns defined by expressions
I understand that it doesnt make sense for insert and update operations, but I'm confused why delete operation is not allowed
Can someone please throw some light on this
Thanks for your help
Thanks
Ravi

Answer 1

If I were to turn this into a delete, which of the six rows of source data would you want to be deleted and why?
SQL> with test_data as
  2      (
  3      select 1 id, 'red' color, 'delete' status from dual union all
  4      select 1 id, 'red' color, 'keep' status from dual union all
  5      select 1 id, 'blue' color, 'delete' status from dual union all
  6      select 1 id, 'blue' color, 'keep' status from dual union all
  7      select 2 id, 'blue' color, 'delete' status from dual union all
  8      select 2 id, 'blue' color, 'keep' status from dual
  9      )
10  select distinct id, color from test_data;
        ID COLO
         1 blue
         1 red
         2 blue