Example

See also: Display Modal Window Messages Using Alerts
 https://www.foxinfotech.in/2015/02/using-single-alert-for-messages-and-confirmation-messages.html

Declare
   al_id       alert;
   al_button   NUMBER;
BEGIN
   al_id := FIND_ALERT ('user_warning');

   IF ID_NULL (al_id)
   THEN
      MESSAGE ('user_warning alert does NOT exist');
      RAISE form_trigger_failure;
   ELSE
      /*
      ** Show the warning alert
      */
      al_button := SHOW_ALERT (al_id);
      /*
      If user pressed OK (button 1) then bring up another alert to confirm -- button mappings are specified in the alert design
      */
      IF al_button = alert_button1
      THEN
         al_id := FIND_ALERT ('are_you_sure');
         IF ID_NULL (al_id)
         THEN
            MESSAGE ('the alert NAMED:are you sure ? does NOT exist');
            RAISE form_trigger_failure;
         ELSE
            al_button := SHOW_ALERT (al_id);
            IF al_button = alert_button2
            THEN
               -- do some task
               erase_all_employee_records;
            END IF;
         END IF;
      END IF;
   END IF;
END;