How important are constraints like NOT NULL and FOREIGN KEY if I'll always control my database input with PHP?

Question

I am trying to create a column in a table that\'s a foreign key, but in MySQL that\'s more difficult than it should be. It would require me to go back and make certain changes

Answer 1

I'm afraid this is a religious topic.

From a puristic point-of-view, you want the database to do the referential integrity. This is ideal when you have a multiplicity of applications accessing the database, because the constraints are in one place. Unfortunately, the real world is not ideal.

If you have to enforce some sort of referential integrity, in my experience, your application will need to know how to do this. This is regardless of whether it is the final arbiter, or the database checks it as well. And even if the database does do the referential integrity, then the application has to know what to do if the database rejects an update, because referential integrity would be violated...

As a sidenote, setting up MySQL to support foreign key constraints is a bit of a process because you need to shift to InnoDB. If you do just that, you can get a lot of performance back by setting innodb_flush_log_at_tx_commit to 1. But it probably would be better if you can instead re-engineer your site to be transaction-aware. Then you get two benefits of InnoDB.