When trying to import data from external sources (which don't have the same input validation in place as the destination tables) you will run into the problem that records or field values don't fit with the table's constraints, see For some unclear reason some records are rejected, or field values not set. This will happen whatever methode you use for importing:
External datasources could be
There is basically only one solution possible, and that is to validate each record and fix any problems before importing that record. 4TOPS Import and Validate essentially is a user interface that supports all activities related to finding problems and fixing them during the import process.