1、GROUP_CONCAT

功能：将group by产生的同一个分组中的值连接起来，返回一个字符串结果。

语法：group_concat( [distinct] 要连接的字段 [order by 排序字段 asc/desc ] [separator '分隔符'] )

说明：通过使用distinct可以排除重复值；如果希望对结果中的值进行排序，可以使用order by子句；separator是一个字符串值，缺省为一个逗号。

1.1 建表

CREATE TABLE `user`  (
  `id` bigint(20) UNSIGNED NOT NULL AUTO_INCREMENT,
  `name` varchar(255) CHARACTER SET utf8mb4 COLLATE utf8mb4_general_ci NOT NULL,
  `age` int(11) NOT NULL,
  PRIMARY KEY (`id`) USING BTREE
) ENGINE = InnoDB AUTO_INCREMENT = 8193 CHARACTER SET = utf8mb4 COLLATE = utf8mb4_general_ci ROW_FORMAT = Dynamic;

-- ----------------------------
-- Records of user
-- ----------------------------
INSERT INTO `user` VALUES (13, '张三3', 13);
INSERT INTO `user` VALUES (14, '张三5', 15);
INSERT INTO `user` VALUES (15, '张三5', 15);
INSERT INTO `user` VALUES (16, '张三3', 13);
INSERT INTO `user` VALUES (17, '张三5', 15);
INSERT INTO `user` VALUES (18, '张三5', 15);
INSERT INTO `user` VALUES (19, '张三3', 13);
INSERT INTO `user` VALUES (20, '张三5', 15);
INSERT INTO `user` VALUES (21, '张三5', 15);
INSERT INTO `user` VALUES (22, '张三3', 13);
INSERT INTO `user` VALUES (23, '张三5', 15);
INSERT INTO `user` VALUES (24, '张三5', 15);

1.2 使用

1.2.1 默认方式

SELECT
	age,
	GROUP_CONCAT( id ) 
FROM
USER 
GROUP BY
	age;
	

返回结果

1.2.2 排序

SELECT
	age,
	GROUP_CONCAT( id ORDER BY id DESC ) 
FROM
USER 
GROUP BY
	age;

返回结果

参考

https://baijiahao.baidu.com/s?id=1595349117525189591&wfr=spider&for=pc