SQL/MySQL/Key/Foreign Key

Define foreign key

Drop table Books;
Drop table Authors;
Drop table AuthorBook;

CREATE TABLE Books (
   BookID SMALLINT NOT NULL PRIMARY KEY,
   BookTitle VARCHAR(60) NOT NULL,
   Copyright YEAR NOT NULL
)
ENGINE=INNODB;
INSERT INTO Books VALUES (1, "Letters", 1934),
                         (2, "Ohio", 1919),
                         (3, "Angels", 1966),
                         (4, "Speaks", 1932),
                         (5, "Man", 1996),
                         (6, "A", 1980),
                         (7, "Card", 1992),
                         (8, "The", 1993);
CREATE TABLE Authors (
   AuthID SMALLINT NOT NULL PRIMARY KEY,
   AuthFN VARCHAR(20),
   AuthMN VARCHAR(20),
   AuthLN VARCHAR(20)
)
ENGINE=INNODB;
INSERT INTO Authors VALUES (1, "Henry", "S.", "Thompson"),
                           (2, "Jack", "Carol", "Oates"),
                           (3, "Red", NULL, "Elk"),
                           (4, "White", "Maria", "Rilke"),
                           (5, "Anne", "Kennedy", "Toole"),
                           (6, "Jane", "G.", "Neihardt"),
                           (7, "Jane", NULL, "Yin"),
                           (8, "Alan", NULL, "Wang");
CREATE TABLE AuthorBook (
   AuthID SMALLINT NOT NULL,
   BookID SMALLINT NOT NULL,
   PRIMARY KEY (AuthID, BookID),
   FOREIGN KEY (AuthID) REFERENCES Authors (AuthID),
   FOREIGN KEY (BookID) REFERENCES Books (BookID)
)
ENGINE=INNODB;
INSERT INTO AuthorBook VALUES (1, 8), 
                              (2, 7), 
                              (3, 6), 
                              (4, 5),
                              (5, 4), 
                              (6, 2), 
                              (8, 1);