Merge records on import

[despens]

Is your feature request related to a problem? Please describe.

When dealing with "messy" data coming from many different sources, currently no RDBMS offers any kind of merging of records, finding and erasing duplicates, pointing out conflicts, etc.

Describe the solution you'd like

On importing data into an existing database, it would be superb if not only it was possible to map columns, but to be alerted of conflicts and giving options to merge or skip entries. Classic example is an address book or CRM system: You want to import a new set of records, yet not create duplicates, instead rather merge in new information into existing records.

Describe alternatives you've considered
A clear and concise description of any alternative solutions or features you've considered.

It is possible to export data, merge outside of the database using OpenRefine or pandas, and then re-import. That's very inefficient.