This is a variant of what's referred to in general database terms as Entity-Attribute-Value or EAV design. It's a bit of a relational database design anti-pattern and should be avoided in most cases. Performance tends to be poor due to the need for many self-joins, and queries are ugly at best.
In PostgreSQL look into the intarray
extension, it should solve your problem pretty ideally if the values are simple integers. Otherwise consider PostgreSQL's standard array types. They've got their own issues, but are generally a lot better than EAV, though they're not lovely to work with from JDBC.
Otherwise, if all you're storing is these vectors, maybe consider a non-relational DB.