Question

I have a MySQL database with these two tables:

Tutor(tutorId, initials, lastName, email, phone, office)
Student(studentId, initials, lastName, email, tutorId)

What is the query to return the initials and last names of any student who share the same tutor?

I tried SELECT intials, lastName FROM Student WHERE tutorId = tutorId but that just returns the names of all students.

Answer 1

You’ll have to join students against itself:

SELECT s1.initials, s1.lastName
FROM Student s1, Student s2
WHERE s1.studentId <> s2.studentID /* Every student has the same tutor as himself */
AND s1.tutorId = s2.tutorid

If you want to output the pairs:

SELECT s1.initials, s1.lastName, s2.initials, s2.lastName
FROM Student s1, Student s2
WHERE s1.studentId <> s2.studentID /* Every student has the same tutor as himself */
AND s1.tutorId = s2.tutorid

To get a list of Tutor – Students:

SELECT tutorId, GROUP_CONCAT( initials, lastName SEPARATOR ', ') 
FROM `Student` 
GROUP BY tutorId
/* to only show tutors that have more than 1 student: */
/* HAVING COUNT(studentid) > 1 */