Final Database Relationship

The complete application works around this relationship:

code text

┌──────────────┐
│   STUDENTS   │
│              │
│ student_id   │
└──────┬───────┘
       │
       │ 1
       │
       │ many
       ▼
┌──────────────┐
│    BORROW    │
│              │
│ borrow_id    │
│ student_id   │
│ book_id      │
│ borrow_date  │
│ return_date  │
└──────┬───────┘
       │
       │ many
       │
       │ 1
       ▼
┌──────────────┐
│    BOOKS     │
│              │
│ book_id      │
│ book_title   │
│ book_author  │
└──────────────┘

The important concept is that borrow does not duplicate student or book information. Instead, it stores their IDs:

code text

student_id → students.student_id
book_id    → books.book_id

This is why the JOIN query is required when displaying readable borrow information. ---

Summary

The application demonstrates three separate CRUD systems.

Students

code text

Create Student
Read Students
Update Student
Delete Student

Books

code text

Create Book
Read Books
Update Book
Delete Book

Borrow

code text

Borrow Book
Read Borrow Records
Return Book
Delete Borrow Record

The most important SQL commands are:

code sql

INSERT
SELECT
UPDATE
DELETE

The most important PDO methods are:

code php

prepare()
execute()
query()
fetch()
fetchAll()

Together, these provide the basic foundation for building PHP applications that interact with MySQL databases using PDO.

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