Database constraints - keep or ignore?

Question

When I was learning in university, they taught us the database fundamentals, basics and rules, and one of the most important rules is the constraints (primary key, foreign key), and how to make 1-m, 1-1, m-n relationships.

Now when I move to real business environment they tell me: you should forget all you have been taught; no constraints, all those relationships are logical, no primary keys, no foreign keys, you can make your constraints through the code.

I don't know who is right: what I learned in my academic life or what I will learn in my new real business life. What do you think?

Answer 1

If somebody told me to ignore keys and constraints on my databases, I would promptly ignore them and go about my business.

Primary keys, foreign keys, and constraints are there for a reason. Use them. They'll make your life easier and your database easier to understand (and, quite often, more performant).

Answer 2

The longer I work with databases, the more I appreciate constraints. In the long run, they save me a lot of time. Only trusted constraints ensure 100% validity of data.

I wrote a chapter on usage of constraints vs. other ways of ensuring data integrity, available as free download here