On: Handling Null Values in Postgres

[derefr]

You realize that joins are a part of the formal definition of relational algebra, while subqueries aren't, right? SQL has had outer joins since the beginning, but subqueries came only gradually, and more limited SQL engines tend still to not support them.

[patrec → derefr]

Why would SQL (fundementaly) need outer joins? "Because it has them", is not really a compelling answer in this context.

A "pure" relational model (like the one C.J. Date has been going on about for decades) has no outer join.