1create table t1(a int(10)unsigned not null auto_increment primary key,
2b varchar(255) not null) engine=innodb default charset=utf8;
3insert into t1 values(1,'aaa'),(2,'bbb');
4alter table t1 auto_increment=1;
5insert into t1 values(NULL, 'ccc');
6select * from t1;
7a	b
81	aaa
92	bbb
103	ccc
11drop table t1;
12