SQL Query Help: Fetching Student Course Information in a Many-to-Many Relationship

Courses
1

Hey folks, I’m trying to wrap my head around many-to-many relationships in MySQL. I’ve got this setup:

  • Students table (id, name, birth_date, dept)
  • Courses table (id, course_name)
  • Enrollments table (student_id, course_id)

I’m stuck on two queries:

  1. How do I get all course names for a specific student?
  2. How can I find students taking at least X number of courses?

Any tips or example queries would be super helpful! I’m pretty new to this and want to get better at handling these kinds of database relationships. Thanks in advance!

2

To fetch all course names for a specific student, you can use this query:

SELECT c.course_name
FROM Courses c
INNER JOIN Enrollments e ON c.id = e.course_id
WHERE e.student_id = [student_id];

For finding students taking at least X courses:

SELECT s.name, COUNT(e.course_id) AS course_count
FROM Students s
INNER JOIN Enrollments e ON s.id = e.student_id
GROUP BY s.id
HAVING course_count >= X;

These queries should work efficiently with your table structure. Remember to replace [student_id] and X with actual values when running the queries. Let me know if you need any clarification on how these work!

3

hey maxrock56, for ur first q try:

SELECT c.course_name
FROM Courses c
JOIN Enrollments e ON c.id = e.course_id
WHERE e.student_id = [specific_student_id];

for the second:

SELECT s.name, COUNT(*) as course_count
FROM Students s
JOIN Enrollments e ON s.id = e.student_id
GROUP BY s.id
HAVING course_count >= X;

hope this helps!

4

Hey MaxRock56! Those are some great questions about many-to-many relationships. :blush:

Have you tried playing around with subqueries yet? They can be super useful for these kinds of problems! For example, to get all course names for a specific student, you could do something like:

SELECT course_name FROM Courses
WHERE id IN (SELECT course_id FROM Enrollments WHERE student_id = [your_student_id]);

As for finding students taking at least X courses, what about using a HAVING clause? Something like:

SELECT s.name FROM Students s
JOIN Enrollments e ON s.id = e.student_id
GROUP BY s.id
HAVING COUNT(DISTINCT e.course_id) >= X;

What do you think? Have you explored these approaches before? I’m curious to hear what you’ve tried so far and what’s working (or not working) for you. Many-to-many relationships can be tricky, but they’re so useful once you get the hang of them!

Do you have any specific use cases in mind for these queries? It might be fun to brainstorm some real-world applications!