mysql一个表中字段保存用逗号分割的用户id，如何将用户id转换成用户名

用户表

测试表，user_ids用户ID

查询结果

CREATE TABLE `user` (
  `id` int(11) NOT NULL COMMENT 'ID',
  `name` varchar(255) COLLATE utf8_bin DEFAULT NULL COMMENT '名称',
  `createtime` datetime DEFAULT NULL COMMENT '创建时间',
  PRIMARY KEY (`id`)
) ENGINE=InnoDB DEFAULT CHARSET=utf8 COLLATE=utf8_bin;

CREATE TABLE `test` (
  `id` int(11) NOT NULL AUTO_INCREMENT,
  `name` varchar(255) COLLATE utf8_bin DEFAULT NULL,
  `user_ids` varchar(255) COLLATE utf8_bin DEFAULT NULL,
  PRIMARY KEY (`id`)
) ENGINE=InnoDB AUTO_INCREMENT=3 DEFAULT CHARSET=utf8 COLLATE=utf8_bin;

SELECT 
	t.id,
	GROUP_CONCAT( u.name ) AS usernames 
FROM
	test t
	LEFT JOIN user u ON FIND_IN_SET( u.id, t.user_ids ) 
GROUP BY
	t.id