SELECT tripad_order, tourad_order
FROM (
    SELECT tripad_order, tourad_order
    FROM tripdetails 
    LEFT JOIN tripaddresses ON tripaddresses.trip_id = tripdetails.trip_id
    LEFT JOIN touraddresses ON touraddresses.tripad_id = 
     tripaddresses.tripad_id AND touraddresses.tour_id = tripdetails.tour_id
    WHERE tripde_id = 39780

    UNION ALL

    SELECT tripad_order, tourad_order
    FROM tripdetails 
    LEFT JOIN touraddresses ON touraddresses.tour_id = tripdetails.tour_id 
    LEFT JOIN tripaddresses ON tripaddresses.tripad_id = 
    touraddresses.tripad_id AND tripaddresses.trip_id IN (0, 
     tripdetails.trip_id)
    WHERE tripde_id = 39780 AND tripad_type IS NOT NULL
) t
GROUP BY tripad_order, tourad_order
ORDER BY 
    CASE WHEN tripad_order = 0 THEN NULL ELSE tripad_order END,
    CASE WHEN tourad_order IS NULL THEN 1 ELSE 0 END, 
    tourad_order;

https://admirable-smakager-729141.netlify.app/post/6