You have a 1-to-many relationship and a many-to-many relationship to deal with. 1 reader to many withdrawals and many readers to many reservations. The book table needs to hold the id of the user who withdrew the book. The reservation needs to be handled with a separate table. This table will have a compound primary key (bookID and reservation date) and a data field (ReaderID). Although a book can only be on loan to a single person at a time, a book may be reserved by many people at a time and the reservations are date sensitive.
You'll need to have a way of notifying people when their reserved book is available (maybe an email). You'll also need a query that runs every day looking for pending reservations so you can get rid of the ones that expire and notify the next person in line.
