PPT Slide
Do we need aliases? The answer is NO, but it is nice to use them if your typing skill is not so good.
select s.studentid, s.studentname, sc.classid
from student s, stud_class sc
where s.studentid = sc.studentid;
select student.studentid,
where student.studentid = stud_class.studentid
order by student.studentname, stud_class.classid;