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When you install Prestashop on a server with Mysql 5.7, you will get an error occured installation process :

"SQL error on query All parts of a PRIMARY KEY must be NOT NULL, if you need NULL in a key, use UNIQUE instead​"

This error will breaks your installation process whether you try to reinstall as many times. Here is the way to fix this problem.

Open your Prestashop-package/install/data/db_structure.sql file :

Find

CREATE TABLE `PREFIX_cart_product`
Look below this line and change PRIMARY KEY to UNIQUE

Save and exit. That's all. Now you can re-install without any problems.