MySQL - Relational tables - How to create multiple relationships?

Question

I have two tables in my database.

Table 1 : book
book_id (Primary & Auto Increment)
book_name
writer_id (Foreign Key from writer table, selected as index)

Table 2 : writer
writer_id (Primary & Auto Increment)
writer_name

I can add only one writer to a book, but a book can be written by two or more writers. How can I achieve that?

I thought I could create two tables called writer_2 and writer_3 (since most books are written by 1, 2 or 3 writers) and add them as a foreign key to my table, but I am open to alternative solutions.

I am using phpmyadmin and my table storage engine is InnoDB.

Answer 1

You need a junction table that assigns writers to books. This would be something like:

create table BookWriter (
    Book_Id int not null,
    Writer_Id int not null,
    foreign key (Book_id) references book(book_id),
    foreign key (Writer_Id) references writer(writer_id)
);

Note that you could have additional information in this table, such as an alias:

create table BookWriter (
    Book_Id int not null,
    Writer_Id int not null,
    Alias varchar(255),
    foreign key (Book_id) references book(book_id),
    foreign key (Writer_Id) references writer(writer_id)
);

For instance, "Kilgore Trout" who wrote a book called "Venus on the Half-Shell" was really Kurt Vonnegut.

Answer 2

What you are looking for is a many-to-many relationship.

Table 3 : bookwriter
writer_id
book_id

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