alter table student rename user;
alter table user modify stu_name varchar(30);
mysql> alter table user change stu_name name varchar(20);
mysql> alter table user cchange stu_sex sex int(2);
mysql> ALTER TABLE user ADD phone VARCHAR(20);
alter table student rename user;
alter table user modify stu_name varchar(30);
mysql> alter table user change stu_name name varchar(20);
mysql> alter table user cchange stu_sex sex int(2);
mysql> ALTER TABLE user ADD phone VARCHAR(20);