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);