CTE's are extensions to try an regain some of what was lost when adopting a model loosely based on Codd's declarative relational algebra, specifically the lack

CTE's are extensions to try an regain some of what was lost when adopting a model loosely based on Codd's declarative relational algebra, specifically the lack of transitive closure, the rest mostly fit into the CRUD world. It is a bit circular, CRUD's elements create, read, update, and delete were chosen to represent the core features of a persistence layer.