I have a question about validations in applications.
See, when we create apps, we always do input validation, thus there wont be any invalid data in our DBs. (assuming the validation is 100% accurate)

And then we use these data for manipulation. For an example , we create an app to collect student marks to compute their grades.

Since our input data is validated 100% , do we have to validate them in the computaion part again?

This is the question I have. Do we need to take extra burden to validate them again when we do computations on the already validated data?


And not to forget eventhough the app validates these data, we can change them in the DB itself (Admins?)
So do we need to validate them again or make them validated in the DB? (if triggers are supported it d be easy I guess.)


Hope you got my question clearly.

Thanks In Advance