Normalization DB

Кестелер

unnormalized — қате кесте (0NF)

student_subjects_1nf — student_id, student_name, subject

students — id, name, group_id

subjects — id, subject_name

student_subject — student_id, subject_id

student_groups — id, group_name, specialty

readers — id, name, phone · authors — id, name

books — id, title, author_id · reader_books — reader_id, book_id

Шарттар: = != > < >= <= like '%...%' and

Ереже: UPDATE және DELETE тек WHERE-пен.

1NF — бір ұяшықта бір мән

2NF — студент, пән, байланыс кестелері бөлек

3NF — group_name → specialty бөлек кестеде

JOIN

select s.name, g.group_name
from students s
join student_groups g
  on s.group_id = g.id;

Байланыс

students.group_id → student_groups.id
student_subject.student_id → students.id
student_subject.subject_id → subjects.id
books.author_id → authors.id

Агрегат: count(*), sum(), avg(), min(), max(), group by.