The Great Work of the scriptorium - the biblioteka shelf project

The time has come to design a full-fledged shelf on your own, combining everything you have learned in the scriptorium. We will build the heart of the lending desk - the wypozyczenia (loans) table, which links books with readers.

What does the wypozyczenia shelf need?

Each loan is one row. We must record:

• id - the primary key, numbered automatically,
• ksiazka_id - which book was borrowed (a required field),
• czytelnik_id - who borrowed it (a required field),
• data_wypozyczenia - when (a required field),
• data_zwrotu - when it was returned (may be empty if the book is still with the reader).

Assembling the project step by step

1. Primary key - we start with

   id INT AUTO_INCREMENT PRIMARY KEY

   . It is a pattern you already know.
2. Required fields -

   ksiazka_id

   ,

   czytelnik_id

   and

   data_wypozyczenia

   must always have a value, so we add NOT NULL.
3. Optional field - we leave

   data_zwrotu

   without NOT NULL, because while the book is on loan it stays empty (NULL).

The finished pattern

1CREATE TABLE wypozyczenia (
2  id INT AUTO_INCREMENT PRIMARY KEY,
3  ksiazka_id INT NOT NULL,
4  czytelnik_id INT NOT NULL,
5  data_wypozyczenia DATE NOT NULL,
6  data_zwrotu DATE
7);

Why is this a good design?

• Each row has a unique identifier thanks to the primary key.
• The required fields protect against incomplete records (a loan without a book makes no sense).
• The optional field (

  data_zwrotu

  ) faithfully reflects reality - until the return happens, it stays empty.

Build this shelf and you will have the foundation of the entire lending desk. This is your Great Work of the scriptorium!