title: Why is negative id or zero considered a bad practice?
body: <p><strong>Why is negative id or zero considered a bad practice when inserting a primary key in a database table?</strong></p>
  
  <p>I think it could be useful in some cases, but people say that it is not recommended, despite the fact that they never say/know why.</p>
  
  <p>So, I was wondering if is there, by definition, some restriction or if it shouldn't have any problem or if is it just a convention and if really there is some restriction about that, why isn't that feature blocked?</p>