示例：
create table `user_info` (
`id` bigint unsigned not null auto_increment comment '自增ID',
`name` varchar(45) not null default '' comment '用户名',
`created_at` datetime(3) NOT NULL DEFAULT CURRENT_TIMESTAMP(3) COMMENT '创建时间',
`updated_at` datetime(3) NOT NULL DEFAULT CURRENT_TIMESTAMP(3) ON UPDATE CURRENT_TIMESTAMP(3) COMMENT '修改时间',
primary key (`id`)
) engine = InnoDB character set = utf8mb4;
mysql> insert into user_info (name) values('letianbiji.com');
mysql> select * from user_info;
+----+----------------+-------------------------+-------------------------+
| id | name | created_at | updated_at |
+----+----------------+-------------------------+-------------------------+
| 1 | letianbiji.com | 2020-06-06 22:29:38.930 | 2020-06-06 22:29:38.930 |
+----+----------------+-------------------------+-------------------------+
可以看到，created_at 和 updated_at 自动生成了。
mysql> update user_info set name = 'letian' where id=1;
mysql> select * from user_info;
+----+--------+-------------------------+-------------------------+
| id | name | created_at | updated_at |
+----+--------+-------------------------+-------------------------+
| 1 | letian | 2020-06-06 22:29:38.930 | 2020-06-06 22:31:26.345 |
+----+--------+-------------------------+-------------------------+
可以看到，updated_at 自动更新了。
这种自动更新的方式仅支持 CURRENT_TIMESTAMP ，不支持其他函数。例如：
-- 下面的 DDL 会报错
create table `user_info_2` (
`id` bigint unsigned not null auto_increment comment '自增ID',
`name` varchar(45) not null default '' comment '用户名',
`created_at` int NOT NULL DEFAULT unix_timestamp() COMMENT '创建时间',
`updated_at` bigint NOT NULL DEFAULT unix_timestamp() ON UPDATE unix_timestamp() COMMENT '修改时间',
primary key (`id`)
) engine = InnoDB character set = utf8mb4;