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Databases

Karenina Braun
Karenina Braun
6,474 Points

Stuck! How do I join three SQL tables to answer these two questions? Or do I not need to?

I'm fairly certain I'll need to join three SQL tables to answer these two questions, but I can't figure it out! Question 1 has me completely stumped, but I think I'm close with question 2. It's important to keep in mind that this database doesn't actually exist, only in theory.

Both Question 1 and 2 use the same tables:

Classes
ID
Name

Students
ID
Name

ClassesStudents
ClassID
StudentID

Question 1: Write a SQL query that will return the name of each class and how many students are taking it.

Question 2: Write a SQL query that will return the names of classes that the student named "John" is taking. Assume there is only one student with that name in the database.

My guess on Question 1 (WIP):*

SELECT ClassesStudents.StudentID, ClassesStudents.ClassID, Classes.Name FROM ClassesStudents, Classes;

*My guess on Question 2:

SELECT Classes.Name FROM Students JOIN ClassesStudents ON ClassesStudents.StudentID=Students.ID AND Students.Name = "John" JOIN Classes ON Classes.ID=ClassesStudents.ClassID

Can anyone please help me out? I've googled everything I could think of :/ If anyone could answer these two questions for me, that would be amazing. I learn by dissecting!

1 Answer

Steven Parker
Steven Parker
231,269 Points

It would be easier to provide a specific answer if you give a link to the course page you're working on.

But in the meantime the "how many" part of the first question is a clue that you'll need an aggregate function to create this as there's no column that has that information already. This might also be a good opportunity to use grouping.