Группировка вывода дочерних разделов в родительские Mysql

SELECT CASE WHEN wash_addr IS NULL THEN city_name
            WHEN bfrs_name IS NULL THEN CONCAT('-',wash_addr)
            ELSE                        CONCAT('--',bfrs_name)
            END name
FROM ( SELECT city.name city_name, null wash_addr, null bfrs_name
       FROM city
     UNION ALL
       SELECT city.name, wash.addr, null
       FROM city
       JOIN wash ON city.pref = wash.city
     UNION ALL
       SELECT city.name, wash.addr, bfrs.name
       FROM city
       JOIN wash ON city.pref = wash.city
       JOIN bfrs ON city.pref = bfrs.city AND wash.id = bfrs.wash
     ) subquery
ORDER BY city_name, wash_addr IS NOT NULL, wash_addr, bfrs_name IS NOT NULL, bfrs_name;

если в каком-то городе нет мойки (или постов) его не выводить. – kilotonna

SELECT CASE WHEN wash_addr IS NULL THEN city_name
            WHEN bfrs_name IS NULL THEN CONCAT('-',wash_addr)
            ELSE                        CONCAT('--',bfrs_name)
            END name
FROM ( SELECT DISTINCT city.name city_name, null wash_addr, null bfrs_name
       FROM city
       JOIN wash ON city.pref = wash.city
       JOIN bfrs ON city.pref = bfrs.city AND wash.id = bfrs.wash
     UNION ALL
       SELECT DISTINCT city.name, wash.addr, null
       FROM city
       JOIN wash ON city.pref = wash.city
       JOIN bfrs ON city.pref = bfrs.city AND wash.id = bfrs.wash
     UNION ALL
       SELECT city.name, wash.addr, bfrs.name
       FROM city
       JOIN wash ON city.pref = wash.city
       JOIN bfrs ON city.pref = bfrs.city AND wash.id = bfrs.wash
     ) subquery
ORDER BY city_name, wash_addr IS NOT NULL, wash_addr, bfrs_name IS NOT NULL, bfrs_name;