What are the student ids of all students who received an enrollment grade of C?
select stu_num from enroll where enroll_grade = 'C'
What are the first names that correspond to each student id?
select stu_fname from student as t1 join enroll as t2 on t1.stu_num = t2.stu_num where enroll_grade = 'C'
What is a list of distinct first names?
select distinct stu_fname from student as t1 join enroll as t2 on t1.stu_num = t2.stu_num where enroll_grade = 'C'