ALTER DATABASE ylyn CHARACTER SET utf8mb4 COLLATE utf8mb4_bin;
ALTER TABLE `user_info` CONVERT TO CHARACTER SET utf8mb4 COLLATE utf8mb4_bin;
ALTER TABLE `user_info` MODIFY COLUMN `nickname`  varchar(255) CHARACTER SET utf8mb4 COLLATE utf8mb4_bin;
SHOW VARIABLES WHERE Variable_name LIKE 'character%' OR Variable_name LIKE 'collation%';