MySQL递归查询所有子节点，树形结构查询

CREATE FUNCTION fn_get_child(rootId INT,deep INT) RETURNS varchar(4000) CHARSET utf8 #rootId为你要查询的节点 #deep 为你要查询的层级
BEGIN
#声明两个临时变量
DECLARE temp VARCHAR(4000);
DECLARE temp_child VARCHAR(4000);
DECLARE n INT DEFAULT 2;
SET temp = '$';
SET temp_child = CAST(rootId AS CHAR);#把rootId强制转换为字符
SET n = deep;
WHILE temp_child is not null DO
SET temp = CONCAT(temp,',',temp_child);#循环把所有节点连接成字符串。
SELECT GROUP_CONCAT(id) INTO temp_child FROM address where FIND_IN_SET(parent_id,temp_child)>0;
set n = n-1;
END WHILE;
RETURN temp;

END