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

Even if your PHP code is perfectly bug-free, it may stop mid-script (out of memory error, segfault in some library, etc), leaving half-inserted stuff in the database, hence the importance of using InnoDB and transactions.

Same for constraints, of course you should have proper form validation, and database constraints behind it to catch bugs.

Database constraints are easy to specify, finding bugs in the application is hard, and even harder without constraints.

My experience has been that improperly constrained databases, and anything that uses MyISAM, WILL have inconssitent data after a few months of use, and it is very hard to find where it came from.