php - Cannot set FK constrains in MySQL


I have a problem that i cant solve right now and i have read similar question but i didnt help me!

I have i Users table and a Books table and i want to set a ONE to ONE relationship between them.

Im trying to set users_id - PK in Users to FK in Books table but it dosent work!

What am i doing wrong?

Please help!

I'll add images for the steps i go through in the same order:

Users table enter image description here

Books table, with users_id as index (Non unique) enter image description here

Setting upp the constrain for FK enter image description here

And at last the ERROR s




It means that you have abooks row that does not have a matchinguser_id in theusers table.

You need to add an user or update the books table first.

If you add a foreign key, you cannot havenull or0 values (forAUTO_INCREMENT keys) in your books.user_id anymore.

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