primarykey

create table student (id int not null);
insert into student values(1);
insert into student values(2);
insert into student values(3);
insert into student values(3);
insert into student values(1);
select*from student;

create table students (code int not null);
insert into students values(1001);
insert into students values(1002);
insert into students values(1003);
insert into students values(1003);
insert into students values(1001);
select* from students;

create table studenta (code int unique);
insert into studenta values(1001);
insert into studenta values(1002);
insert into studenta values(1003);
select* from studenta;

create table studente (code int, name varchar(20) not null unique,age int not null unique );
insert into studente values(1001,'vasu',22);
insert into studente values(1002,'vase',24);
insert into studente values(1003,'vasy',25);
select age,name,code from studente;