declare
  l_str varchar2(300);
begin	
  if checkbox_checked('cb_select') then
     l_str := 'grant  select on ' || :table_name || ' to '   || :user_name;
  else
     l_str := 'revoke select on ' || :table_name || ' from ' || :user_name;
  end if;
  
  forms_ddl(l_str);
  
  if not form_success then 
     message ('Operation failed'); 
  else 
     message ('Operation succeeded'); 
  end if;
end;

select count(*) from scott.test;