A million times this. Cleaning up bad data after the fact can actually be impossible. When it is possible, it can be annoying, tedious, and easy to fuck up. A

A million times this. Cleaning up bad data after the fact can actually be impossible. When it is possible, it can be annoying, tedious, and easy to fuck up. All of this can be avoided by an astonishingly small amount of forward thinking. What columns should not be nullable? What are the maximum sizes needed for strings, numbers, and binary data? Which columns or sets of columns should only ever be inserted once? What columns point to other rows, should they be required, and what should happen if one side or the other has deletion attempted? Constraints should cover basic data consistency guarantees. Validations are fine for business logic and business requirements, since those might change more frequently.