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

1. I don't think you can be certain that your database will only be accessed by PHP and if so, by developers who will use it to respect those constraints for the entire lifecyle of your database.

2. If you include these constraints in your schema, then one can get a good idea of how the data is used and related by investigating your schema. If you only put all that in the code, then someone would have to look in both the database and the PHP code.

But shouldn't that stuff be in the design documentation, data dictionary, and logical database design?

Yes, but these documents are notorious for getting out of date and stale. I know you would never allow that to happen, but some people who have experience with projects with less discipline may assume this about your project, and want to consult the actual code and schema rather than documentation.