为什么第一行sno前要加student.？

Question

select student.sno,sname,cname,grade
from student,course,enroll
where student.sno＝enroll.sno and course.cno=enroll.cno and (cname＝'数据库'or cname="操作系统)；

Answer 1

为了更好的区分究竟是 student表的sno还是 course表的sno，还是 enroll表的sno