Test MySQL ALTER TABLE for timestamp column.

cars.sql

drop table if exists `cars`;

create table `cars` (
  `id` int not null auto_increment,
  `make` varchar(255),
  `model` varchar(255),
  `created_at` timestamp default current_timestamp not null,
  `updated_at` timestamp default current_timestamp on update current_timestamp not null,
  primary key (`id`)
);

insert into `cars` (`make`, `model`) values ('Honda', 'Accord');

select * from `cars`;

select `updated_at` from `cars`;

alter table `cars`
  modify `created_at` timestamp(6)
  default current_timestamp(6) not null;

alter table `cars`
  modify `updated_at` timestamp(6)
  default current_timestamp(6) on update current_timestamp(6) not null;

insert into `cars` (`make`, `model`) values ('Toyota', 'Aurion');

select * from `cars`;

select `created_at`, microsecond(`created_at`) as 'microsecond' from `cars`;