There is also a maintenance cost by putting restraints on the database as almost assuredly your application will have similar constraints. Therefore if those co

There is also a maintenance cost by putting restraints on the database as almost assuredly your application will have similar constraints. Therefore if those constraints change the workload is not just doubled because you have to update the application in two places. But perhaps tripled or more as the developer tries to find any other locations where the same logic might have been put as well. If the logic is in two places it might very well be in three or more.