Library design

Design a tiny library database:

• books — book_id INTEGER PRIMARY KEY, title VARCHAR NOT NULL, isbn VARCHAR UNIQUE, copies INTEGER DEFAULT 1 (never negative)
• members — member_id INTEGER PRIMARY KEY, name VARCHAR NOT NULL
• loans — loan_id INTEGER PRIMARY KEY, book_id and member_id (both required, both foreign keys), issued_on DATE NOT NULL, returned_on DATE that, when present, is not before issued_on