Create Table employees (
id int primary key auto_increment,
first_name VARCHAR(64),
last_name VARCHAR(64)
);
Create Table books (
id int primary key auto_increment,
name VARCHAR(64),
genre_id int,
author VARCHAR(64),
year int
);
Create Table books_genres (
id int primary key auto_increment,
genre_name VARCHAR(64)
);
Create Table users (
id int primary key auto_increment,
first_name VARCHAR(64),
last_name VARCHAR(64)
);
Create Table orders (
id int primary key auto_increment,
employee int,
user int,
book int,
get_at date,
return_at date
);
insert into orders (employee, user, book, get_at, return_at)
values
(1, 2, 3, '2022-01-09', '2022-01-15'),
(3, 4, 5, '2022-01-18', null);
select
orders.*,
DATEDIFF(COALESCE(return_at, CURRENT_DATE), get_at) days_in_rent
from orders;