create table t(id int primary key, a int) engine=InnoDB;
insert into t (id, a) values (1, 1);
alter table t modify column id int auto_increment;
check table t;
Table	Op	Msg_type	Msg_text
test.t	check	status	OK
insert into t (a) values (2);
alter table t modify column id int, algorithm=instant;
check table t;
Table	Op	Msg_type	Msg_text
test.t	check	status	OK
insert into t (id, a) values (3, 3);
select * from t;
id	a
1	1
2	2
3	3
check table t;
Table	Op	Msg_type	Msg_text
test.t	check	status	OK
drop table t;