MySQL递归查找树形结构(这个方法太实用了!)

CREATE TABLE `city` (
`i_id`  int(11) NOT NULL AUTO_INCREMENT ,
`p_id`  int(11) NULL DEFAULT NULL ,
`c_name`  varchar(50) CHARACTER SET utf8 COLLATE utf8_general_ci NULL DEFAULT NULL ,
PRIMARY KEY (`i_id`)
)
ENGINE=InnoDB
DEFAULT CHARACTER SET=utf8 COLLATE=utf8_general_ci
AUTO_INCREMENT=11
ROW_FORMAT=COMPACT;

SELECT GROUP_CONCAT(i_id)
FROM city
WHERE p_id='2'

SELECT * FROM city
WHERE FIND_IN_SET(p_id,'1,4')

SELECT GROUP_CONCAT(i_id) AS ids
FROM city
WHERE p_id=1;

CREATE DEFINER = `root`@`localhost` FUNCTioN `getSubnodes`(param_i_id  int)
 RETURNS varchar(100)
BEGIN
 
#输入I_ID 输出此I_ID下的所有子节点(只有一级)
 
  DECLARE strSubIds VARCHAR(100);
  DECLARE strPid VARCHAR(100);
  SET strSubIds = '$';
  SET strPid =cast(param_i_id as CHAR);
  SELECT GROUP_CONCAT(i_id) INTO strSubIds FROM city WHERE p_id=strPid;
  RETURN strSubIds;
END;

CREATE DEFINER = `root`@`localhost` FUNCTION `getAllSubNodes`(`param_i_id` int)
 RETURNS varchar(100)
BEGIN
 
DECLARE strAllSubIds VARCHAR(100);
DECLARE strTempPid VARCHAR(100);
 
#先得到第一级,也可以掉用getSubNodes(param_i_id);
 
# SELECT GROUP_CONCAT(i_id) INTO strAllSubIds FROM city WHERE p_id=param_i_id;
 SET strAllSubIds = getSubNodes(param_i_id);
SET strTempPid = strAllSubIds;
 
#根据 strTempPid 判断是否还有子节点
 
WHILE strTempPid is not null DO
SELECT group_concat(i_id) INTO strTempPid FROM city WHERE FIND_IN_SET(p_id,strTempPid)>0;
 
#需要对strTempPid判断,非空用 , 连接
 
IF (strTempPid is not NULL) THEN
SET strAllSubIds = concat(strAllSubIds,',',strTempPid);
 
END IF;
END WHILE;
RETURN strAllSubIds;
END;