A.SELECT课程名称,COUNT(学号)AS选修人数FROM学生,课表WHERE学生.课程编号=课表.课程编号: GROUP BY课程名称HAVING COUNT(*)>=50 ORDER BY COUNT(学号)ASC B.SELECT课程名称,COUNT(学号)AS选修人数FROM学生,课表WHERE学生.课程编号=课表.课程编号;GROUP BY课程名称HAVING COUNT(*)>=50 ORDER BY COUNT(学号)DESC C.SELECT课程名称,COUNT(学号)AS选修人数FROM学生,课表WHERE学生.课程编号=课表.课程编号: GROUP BY课程名称HAVING COUNT(*)>=50 ORDER BY选修人数ASC D.SELECT课程名称,COUNT(学号)AS选修人数FROM学生,课表WHERE学生.课程编号=课表.课程编号: GROUP BY课程名称HAVING COUNT(*)>=50 ORDER BY选修人数DESC