单纯MYSQL递归查询上下级关系

查询 id = 6 的所有父级

SELECT ID.level, DATA.* FROM( 
SELECT 
@id as _id, 
( SELECT @id := parent_id 
FROM table1 
WHERE id = @id 
) as _pid, 
@l := @l+1 as level 
FROM table1, 
(SELECT @id := 6, @l := 0 ) b 
WHERE @id > 0 
) ID, table1 DATA 
WHERE ID._id = DATA.id 
ORDER BY level;

根据这个父级查询方法，很容易可以写出查所有子级的，下面的查询 id=3 的所有子级

SELECT ID.level, DATA.* FROM( 
SELECT 
@ids as _ids, 
( SELECT @ids := GROUP_CONCAT(id) 
FROM table1 
WHERE FIND_IN_SET(parent_id, @ids) 
) as cids, 
@l := @l+1 as level 
FROM table1, 
(SELECT @ids :=3, @l := 0 ) b 
WHERE @ids IS NOT NULL 
) id, table1 DATA 
WHERE FIND_IN_SET(DATA.id, ID._ids) 
ORDER BY level, id