MYSQL树结构，查询所有子元素ID，函数

-- ppid参数(因为和下边pid重复)，查询sql自行替换，数据库名自行替换

CREATE DEFINER=`by`@`%` FUNCTION `getUserChilds`(`ppid` INT) RETURNS varchar(4000) CHARSET utf8
    NO SQL
BEGIN
    DECLARE sTemp VARCHAR(4000);
    DECLARE sTempChd VARCHAR(4000);
    
    SET sTemp=‘‘;
    SET sTempChd = CAST(ppid AS CHAR);
    WHILE sTempChd IS NOT NULL DO
    SET sTemp= CONCAT(sTemp,‘,‘,sTempChd);
    SELECT GROUP_CONCAT(id) INTO sTempChd FROM by_user WHERE FIND_IN_SET(pid,sTempChd)>0;
    END WHILE;
    RETURN sTemp ;
END

-- 返回的是 ‘1,2,3,4,5‘ 的字符串
-- pid参数， 查询sql如下：
select * from user bul where FIND_IN_SET(id, getUserChilds(pid))