Bagaimana menerapkan hubungan satu-ke-satu, satu-ke-banyak dan banyak-ke-banyak saat mendesain tabel?

Satu-ke-satu: Gunakan kunci asing ke tabel yang direferensikan:

student: student_id, first_name, last_name, address_id
address: address_id, address, city, zipcode, student_id # you can have a
                                                        # "link back" if you need

Anda juga harus meletakkan batasan unik pada kolom kunci asing (addess.student_id ) untuk mencegah beberapa baris dalam tabel anak (address ) dari menghubungkan ke baris yang sama dalam tabel yang direferensikan (student ).

Satu-ke-banyak :Gunakan kunci asing di banyak sisi hubungan yang menautkan kembali ke sisi "satu":

teachers: teacher_id, first_name, last_name # the "one" side
classes:  class_id, class_name, teacher_id  # the "many" side

Banyak-ke-banyak :Gunakan tabel persimpangan (contoh):

student: student_id, first_name, last_name
classes: class_id, name, teacher_id
student_classes: class_id, student_id     # the junction table

Contoh kueri:

 -- Getting all students for a class:

    SELECT s.student_id, last_name
      FROM student_classes sc 
INNER JOIN students s ON s.student_id = sc.student_id
     WHERE sc.class_id = X

 -- Getting all classes for a student: 

    SELECT c.class_id, name
      FROM student_classes sc 
INNER JOIN classes c ON c.class_id = sc.class_id
     WHERE sc.student_id = Y