Which students did receive an A in any courses?
select * from student as t1 join enroll as t2 on t1.stu_num = t2.stu_num where t2.enroll_grade = 'A'
Who of them also received a C in any courses?
select * from student as t1 join enroll as t2 on t1.stu_num = t2.stu_num where t2.enroll_grade = 'C' or t2.enroll_grade = 'A'
What are their' first names and last names?
select t1.stu_fname, t1.stu_lname from student as t1 join enroll as t2 on t1.stu_num = t2.stu_num where t2.enroll_grade = 'C' or t2.enroll_grade = 'A'