The usual way of implementing a multivalued attribute in a relational database is to put it in a separate table with the primary key (maintable_id, multivalued). I have the multivalued attribute Year. Following the rule, I create a new table year which has the primary key of the main table combined with year as an identifier.
It works but doesn't feel right as I have to save a year redundantly, even though it is just a limited amount of years (e.g. 2020 would be saved separately many times for each occurrence of the main table). Is there a better way to model that?