foreign key

Question

What is the purpose of foreign key?
Lets say that we have 2 tables author and book:

https://code.sololearn.com/ca7a2A3a23a9

Why we need the foreign key in the book table? Wouldn't be easier if we replace the `author_id` foreign key with `author_name` and we don't need the author table anymore?

Let say I want to add a new book to the database, first I need to check if the author is in the `author` table if it isn't I have to add it and then add the book.

Answer 1

If I got your question right, you are asking, why one should use foreign key.
Table: user
Name
Email
...
Table: post
Text
Date
Author (=user)

If you put table post Author = id, it works fine, but if you want to render the data later on, you would have to query two tables - or 100 tables - to get the data you want to render. (For example you.
want to render:
post.text and user.email)
But if you put a foreignkey you just query one table (post) and then you can access the data like:
post.text
post.author.email (author = user as foreignkey)

(That's what I think, to know about that :))