begin
  execute immediate 'drop role owb_d_%user';
exception
  when others
  then
    null;
end;
/
commit;

begin
  execute immediate 'drop role owb_o_%user';
exception
  when others
  then
    null;
end;
/
commit;

begin
  execute immediate 'drop role owb_a_%user';
exception
  when others
  then
    null;
end;
/
commit;