SQL Query Help

Please post an explanation with your answer.

Given the following relational database schema:

Student = (SSN, Name, Major)

Course = ( CourseNumber, PrerequisiteCourseNumber, Course Title, NumberUnits)

Section = ( CourseNumber, Quarter, RoomNumber, DayTime), where DayTime is of the form MW 1:0-2:00PM.

Enrollment = (SSN,CourseNumber, Quarter, Grade)// Grade is either Null or a letter grade.

1. List the name and major of every student who has only taken courses that meet MW afternoon (12 or after).

Is the following query correct?

SELECT DISTINCT s.Name, s.major FROM sys.student s LEFT JOIN sys.enrollment e ON s.ssn=e.ssn LEFT JOIN sys.section sec ON e.CourseNumber=sec.CourseNumber WHERE NOT EXISTS (SELECT * FROM sys.section sec2 WHERE sec.DayTime=sec2.DayTime AND sec2.DayTime NOT LIKE 'MW%PM')

2. List the name and major of every student who has taken all the courses that meet MW afternoon.

3.List the name and major of every student who has not taken any course that meets MW afternoon.

4.List every CoursaeNumber and Quarter which has the highest enrollment.

5.List every CourseNumber and CourseTitle which has the highest enrollment based on all quarters.