Currently, I'm involved in an assignment that requires the management of a collection of PostgreSQL databases related to a school district. One of my tasks is to update the new field student_gpas, which is an array designed to store unique student GPAs. To accomplish this using Python and SQLAlchemy, I have written the following code:
schools = db.session.query(School).filter(school.is_selected == true).all()
For sch in schools:
grades = db.session.query(Grade).filter(grade.school_id == sch.id).all()
For gr in grades:
classes = db.session.query(Class).filter(class.grade_id == grades.id).all()
For cl in classes:
students = db.session.query(Student).filter(student.class_id == cl.id).all()
For st in students:
If st.gpa not in gr.student_gpas:
gr.student_gpas.append(st.gpa)
If I were to transform this code snippet into one lengthy and intricate SQL statement, what would be the ideal approach?