Mysql 父子集查詢

1.通過子查詢父集

SELECT T2.*
    FROM ( 
    SELECT 
        @r AS _id, 
        (SELECT @r := parent_code FROM city_info WHERE city_code = _id) AS parent_id, 
        @l := @l + 1 AS lvl 
    FROM 
        (SELECT @r := 110101, @l := 0) vars, 
        city_info h 
    WHERE @r <> 0) T1 
JOIN city_info T2 
ON T1._id = T2.city_code
ORDER BY T1.lvl DESC 

2.通過父查詢子集

SELECT 
    T2.* 
    FROM ( 
        SELECT 
        @ids as _ids, 
        ( SELECT @ids := GROUP_CONCAT(city_code) 
            FROM city_info 
            WHERE FIND_IN_SET(parent_code, @ids) 
        ) as cids, 
            @l := @l+1 as lvl 
        FROM city_info, 
            (SELECT @ids :=110100, @l := 0 ) b 
        WHERE @ids IS NOT NULL 
    ) city_code, city_info T2 
WHERE FIND_IN_SET(T2.city_code, _ids) 
ORDER BY lvl, city_code