I have a csv file which contains: 

MyProvider / External ID, Address / Street, Address / PostalCode

The relation between providers and addresses is Many2many and I want to add more providers to an existing address.

If import is succesful many different addresses with the same street and postal code are created which is bad.

If I do street and postalcode unique using _sql_constraints and import first the addresses and then I try to import update them Odoo will throw an error because the addresses can't be found just by their street names.

Maybe the solution it's obvious, sorry I'm new with Odoo.