环境
//MySQL client
select version();
5.7.28-log
SHOW VARIABLES WHERE Variable_name LIKE 'character\_set\_%' OR Variable_name LIKE 'collation%';
character_set_client utf8mb4 //
character_set_connection utf8mb4
character_set_database utf8mb4 //
character_set_filesystem binary
character_set_results utf8mb4
character_set_server utf8
character_set_system utf8
collation_connection utf8mb4_general_ci
collation_database utf8mb4_general_ci
collation_server utf8_general_ci
数据库的默认的CHARACTER SET 是utf8mb4，collation 是utf8mb4_general_ci。
表结构
//建表语句
CREATE TABLE `test` (
`id` bigint(20) NOT NULL,
`code` varchar(50) NOT NULL,
PRIMARY KEY (`id`)
) ENGINE=InnoDB DEFAULT CHARSET=utf8mb4 COMMENT='test';
insert into test values(1,'A');
insert into test values(2,'a');
collation为utf8mb4_general_ci是大小写不敏感的，修改成utf8mb4_bin。
修改字段SQL如下
ALTER TABLE `test` CHANGE `code` `code` varchar(20) CHARACTER SET utf8mb4 COLLATE utf8mb4_bin not null;
