create table students (name varchar (32), class varchar (32), grade char (2));
insert into students values ('John', 'Math', 'A');
insert into students values ('Mary', 'Math', 'A');
insert into students values ('Tom', 'Math', 'C');
insert into students values ('Tom', 'English', 'C+');
insert into students values ('John', 'English', 'A');
insert into students values ('Mary', 'English', 'B');
insert into students values ('Tom', 'Science', 'D-');
insert into students values ('John', 'Science', 'A');
insert into students values ('Mary', 'Science', 'B+');
