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

The most important thing about using NOT NULL to me, is more the documentation part. When I return to the project after a few months I forget which columns it is acceptable to have nulls in. If the column says NOT NULL, then I know I will never ever have to deal with potential null values from it. And if it allows null, then I know for sure I have to deal with them.

The other thing is, as others have noted: You may miss something somewhere, and cleaning up data sucks, or may be entirely impossible. It's better to know for sure that all data in your database is consistent.