【MySQL将字段值逗号分隔的数据分成多行，更新后，再合并为一行】

1、如图把TEST1的F_G2替换成TEST2的F_G2，同时更新F_G3

2、两个测试表的sql

SET NAMES utf8mb4;
SET FOREIGN_KEY_CHECKS = 0;

-- ----------------------------
-- Table structure for TEST1
-- ----------------------------
DROP TABLE IF EXISTS `TEST1`;
CREATE TABLE `TEST1`  (
  `F_G1` varchar(255) CHARACTER SET utf8mb4 COLLATE utf8mb4_unicode_ci NOT NULL,
  `F_G2` varchar(255) CHARACTER SET utf8mb4 COLLATE utf8mb4_unicode_ci NULL DEFAULT NULL,
  `F_G3` varchar(255) CHARACTER SET utf8mb4 COLLATE utf8mb4_unicode_ci NULL DEFAULT NULL,
  `F_G4` varchar(255) CHARACTER SET utf8mb4 COLLATE utf8mb4_unicode_ci NULL DEFAULT NULL,
  PRIMARY KEY (`F_G1`) USING BTREE
) ENGINE = InnoDB CHARACTER SET = utf8mb4 COLLATE = utf8mb4_unicode_ci ROW_FORMAT = Dynamic;

-- ----------------------------
-- Records of TEST1
-- ----------------------------
INSERT INTO `TEST1` VALUES ('1', '1', '', '备注1');
INSERT INTO `TEST1` VALUES ('2', '1,2', '', '备注1');
INSERT INTO `TEST1` VALUES ('3', '1,3', '', '备注1');
INSERT INTO `TEST1` VALUES ('4', '2,3', '', '备注1');
INSERT INTO `TEST1` VALUES ('5', '3', '', '备注1');
INSERT INTO `TEST1` VALUES ('6', '2,3,4', '', '备注1');
INSERT INTO `TEST1` VALUES ('7', '1,3,4', '', '备注1');

-- ----------------------------
-- Table structure for TEST2
-- ----------------------------
DROP TABLE IF EXISTS `TEST2`;
CREATE TABLE `TEST2`  (
  `F_G1` varchar(255) CHARACTER SET utf8mb4 COLLATE utf8mb4_unicode_ci NOT NULL,
  `F_G2` varchar(255) CHARACTER SET utf8mb4 COLLATE utf8mb4_unicode_ci NULL DEFAULT NULL,
  `F_G3` varchar(255) CHARACTER SET utf8mb4 COLLATE utf8mb4_unicode_ci NULL DEFAULT NULL,
  `F_G4` varchar(255) CHARACTER SET utf8mb4 COLLATE utf8mb4_unicode_ci NULL DEFAULT NULL,
  PRIMARY KEY (`F_G1`) USING BTREE
) ENGINE = InnoDB CHARACTER SET = utf8mb4 COLLATE = utf8mb4_unicode_ci ROW_FORMAT = Dynamic;

-- ----------------------------
-- Records of TEST2
-- ----------------------------
INSERT INTO `TEST2` VALUES ('1', '01', '生活', '1');
INSERT INTO `TEST2` VALUES ('2', '02', '金钱', '2');
INSERT INTO `TEST2` VALUES ('3', '03', '生命', '3');
INSERT INTO `TEST2` VALUES ('4', '04', '时间', '4');

SET FOREIGN_KEY_CHECKS = 1;

3、先将TEST1的F_G2进行分割，行转列

-- 分割后的内容
SELECT
a.F_G2,
		-- /*先正着取出几部分*/，然后在此基础再倒着取出最后那一部分
substring_index( substring_index(a.F_G2,',',b.help_topic_id + 1),',' ,- 1  ) AS new_F_G2
from 
-- 将原数据先取出来  like中的符号与实际表里字段中的分割符对应
(select F_G1,F_G2,F_G3,F_G4 from TEST1 where F_G2 like '%,%') a  -- 如果表内还存在没有分隔符，就单个值的则直接select sname,sage from student 就行，总之目的是取出要处理的数据
join mysql.help_topic b ON  -- mysql帮助表 内含字符等 ，help_topic_id是从0开始的，其实使用的是它的计数功能 
b.help_topic_id < ( length(a.F_G2) - length(REPLACE (a.F_G2, ',', ''))  + 1 ); -- 实际算出的是分割后总共有几部分（此处是将长度为1的英文状态替换成空）

4、根据关联表，查询合并新值

-- 分割后关联Test2表，进行合并更新
select 
A.*,
TEST2.*,
group_concat(TEST2.F_G2) NEW_HB_F_G2,
group_concat(TEST2.F_G3)NEW_HB_F_G3
from (
		SELECT
		a.F_G1,
		a.F_G2,
		a.F_G3,
		a.F_G4,
		substring_index( substring_index(a.F_G2,',',b.help_topic_id + 1),',' ,- 1  ) AS new_F_G2
		from (select F_G1,F_G2,F_G3,F_G4 from TEST1 where F_G2 like '%,%') a 
		join mysql.help_topic b ON 
		b.help_topic_id < ( length(a.F_G2) - length(REPLACE (a.F_G2, ',', ''))  + 1 )
)A
left join TEST2 on TEST2.F_G4 = A.new_F_G2
group by A.F_G1;

5、把TEST1的F_G2和F_G3更新成新合并的数值

-- 把TEST1的F_G2和F_G3更新成新合并的数值
UPDATE (
		select 
		A.F_G1,
		group_concat(TEST2.F_G2) NEW_HB_F_G2,
		group_concat(TEST2.F_G3)NEW_HB_F_G3
		from (
				SELECT
				a.F_G1 F_G1,-- 可以关联的列
				a.F_G2,-- 被拆分的列
				substring_index( substring_index(a.F_G2,',',b.help_topic_id + 1),',' ,- 1  ) AS new_F_G2 -- 需要拿到的值
				from (select F_G1,F_G2,F_G3,F_G4 from TEST1 where F_G2 like '%,%') a 
				join mysql.help_topic b ON 
				b.help_topic_id < ( length(a.F_G2) - length(REPLACE (a.F_G2, ',', ''))  + 1 )
		)A
		left join TEST2 on TEST2.F_G4 = A.new_F_G2
		group by A.F_G1
) B ,TEST1 C SET C.F_G2 = B.NEW_HB_F_G2,C.F_G3 = B.NEW_HB_F_G3 WHERE B.F_G1 = C.F_G1;