I think what you're describing is already present as of SQL 2003 in the form of multisets: http://farrago.sourceforge.net/design/CollectionTypes.html http://fa

I think what you're describing is already present as of SQL 2003 in the form of multisets: http://farrago.sourceforge.net/design/CollectionTypes.html http://farrago.sourceforge.net/design/CollectionTypes.html However, good luck finding a database engine that necessarily supports such features. Some support array types, but I haven't seen too many that support multisets.