Mysql genealogy table to query all descendants of a person

CREATE TABLE `people` (
    `id` INT(11) NOT NULL,
    `name` VARCHAR(50) NULL DEFAULT NULL,
    `pid` INT(11) NOT NULL DEFAULT '0',
    PRIMARY KEY (`id`)
);
 
CREATE DEFINER=`root`@`%` PROCEDURE `getChildren`(IN `parentId` INT)
    LANGUAGE SQL
    NOT DETERMINISTIC
    CONTAINS SQL
    SQL SECURITY DEFINER
    COMMENT '获取某人所有后代'
BEGIN
    #存放结果的临时表
    DROP TABLE IF EXISTS children;
    CREATE TEMPORARY TABLE children SELECT 0 pLevel,p.* FROM `people` p WHERE id=parentId;
    #存放中间结果的临时表
    DROP TABLE IF EXISTS tem;
    CREATE TEMPORARY TABLE tem SELECT id FROM `people` limit 0;
     
    #逐级填充后代
    SET @pLevel=1;
    REPEAT
        #清空上次数据
        TRUNCATE TABLE tem;
        #将当前level的后代id放入临时表
        INSERT INTO tem SELECT p.id FROM `people` P, children c 
            WHERE p.pid=c.id AND    c.pLevel=(@pLevel-1);
        #将当前level的后代数据塞入结果临时表
        INSERT INTO children SELECT @pLevel pLevel,p.* FROM `people` p, tem t 
        WHERE p.id=t.id;
        SET @pLevel=@pLevel+1;
    UNTIL NOT EXISTS (SELECT * FROM tem) OR @pLevel > 10
    END REPEAT;
     
    #调整表结构，删除临时列和不需要的数据
    ALTER TABLE children DROP COLUMN pLevel;
    DELETE FROM children WHERE id=parentId;
     
    #返回结果
    SELECT * from children;
END