Many-to-many database relationship magento

You should create a table to hold the relation.
So you have your book table which is actually the products table and the author table with id, name, ... and you need an other one that holds the book_id and the author_id and maybe a position so you know in which order to list the authors.

I can recommend you this extension. It will create the code needed to administer and list the authors and allows you to link it many to many with the products.

See the documentation for product relations

• https://github.com/tzyganu/UMC1.9/wiki/crud
• https://github.com/tzyganu/UMC1.9/wiki/product-relation

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_{Note: I am involved in the development of the extension but it's free to use for everyone}