Ask HN: Is there a DB that allows for remote list concatenation?

Not in SQL because my data is not relational and not embedded but remote, what DB provides an API where I can say, you know those lists (of data) I gave you and you gave me back a list of IDs and those were list IDs? I need you now to concatenate these two (ID1, ID2) because from now on I want to be able to consider them as one and the same list. I want to be able to consider the first list ID to be the canonical one.

Is there a DB that allows for "remote list concatenation"?