mysql 递归查询的方法

CREATE TABLE `class` (
`classid` int(11) NOT NULL AUTO_INCREMENT,
`banji` int(11) DEFAULT NULL COMMENT '0',
`nianji` varchar(255) DEFAULT NULL,
PRIMARY KEY (`classid`)
) ENGINE=InnoDB AUTO_INCREMENT=11 DEFAULT CHARSET=utf8;

-- ----------------------------
-- Records of class
-- ----------------------------
INSERT INTO `class` VALUES ('1', '0', '1');
INSERT INTO `class` VALUES ('2', '1', '2');
INSERT INTO `class` VALUES ('3', '1', 'f');
INSERT INTO `class` VALUES ('4', '2', 'd');
INSERT INTO `class` VALUES ('5', '3', 's');
INSERT INTO `class` VALUES ('6', '0', 'a');
INSERT INTO `class` VALUES ('7', '6', 'q');
INSERT INTO `class` VALUES ('8', '7', 'h');
INSERT INTO `class` VALUES ('9', '5', '额');
INSERT INTO `class` VALUES ('10', '4', '121');

SELECT * from class WHERE classid =1
UNION
SELECT * FROM class where banji in(SELECT classid from class  WHERE classid =1 )
UNION
SELECT * FROM class where banji in (SELECT classid FROM class where banji in(SELECT classid from class  WHERE classid =1))

CREATE FUNCTION `selectTree`(`id` int)
RETURNS varchar(2000)
BEGIN
#Routine body goes here...
DECLARE st VARCHAR(4000);
DECLARE	stcc VARCHAR(2000);
#给st赋初值不能null，null会没有返回值
set st='';
set stcc=id;
#判断stcc的是否为null
WHILE stcc is not NULL DO
#拼接字符串赋值给st
SET st=CONCAT(st,',',stcc);
SELECT GROUP_CONCAT(classid) INTO stcc FROM class where FIND_IN_SET(banji,stcc)>0;
END WHILE;
RETURN st;
END;

调用函数查出结果

SELECT * from  class where classid in (SELECT a.ban FROM class a,class b where a.banji=b.classid)  and banji=0