title: Many to Many Self referencing relationship
body: <p>I'm attempting to create a library database using SQL in which one book_id recommends another book_id number. </p>
  
  <p>The table I have created is as follows:</p>
  
  <pre><code>   CREATE TABLE BOOK (
     Book_id INT NOT NULL,
     Book_name VARCHAR(40) NOT NULL,
     Description VARCHAR (100) NOT NULL,
     Image BLOB NOT NULL,
     Category_id INT NOT NULL,
     PRIMARY KEY (Book_id),
     FOREIGN KEY (Category_id) REFERENCES Category (Category_id)
  </code></pre>
  
  <p>Do I need to create a separate table in order to enforce this many to many self relationship?</p>