oracle中添加删除主键的方法

create table student (
studentid int primary key not null,
studentname varchar(8),
age int);

create table students (
studentid int ,
studentname varchar(8),
age int,
constraint yy primary key(studentid));

alter table students drop constraint yy;

SELECT * from user_cons_columns;

alter table student drop constraint SYS_C002715;

alter table student add constraint pk_student primary key(studentid);