Notes: Foreign keys in MySQL automatically create an index on the table. In this example index fk_books_author_id will be created at column books.author_id.; Setting FOREIGN_KEY_CHECKS disables ...

PDO is PHP Data Objects which is used to connect to any database. Benefit of using PDO is that if there is any problem in our query it has an exception class to handle it. If any exception thrown to ...

Foreign keys can refer to another column in the same table. The top-level folder might need to be its own parent - I don't know if it'll let you have a NULL there.