Question

How a query can b done using joins. i am new in database. this query is working fine..
but i want to make it more rubust

   $query = "SELECT student_id 
FROM students
WHERE student_id
IN (
    SELECT student_id
    FROM class_students
    WHERE class_id
        IN (
            SELECT class_id
            FROM class_course
            WHERE teacher_id =". $_SESSION['teacher_id']."))";

is there anyother way to do that

Answer 1

Using IN can be converted to proper joins:

SELECT s.student_id 
FROM students s
JOIN class_students cs ON cs.student_id = s.student_id
JOIN class_course c ON c.class_id = cs.class_id
WHERE teacher_id = ?

Note that I have removed the (irrelevant) application language specifics (perl?) to leave just the SQL that answers the question.