I agree the children entity ID must be already unique without having to use the parent entity id. It's just that in my experience have the children table prima

I agree the children entity ID must be already unique without having to use the parent entity id. It's just that in my experience have the children table primary b-tree sorted on ParentID then childrenID make join much more efficient unless you can use table interleaving like in Google SpannerDB https://cloud.google.com/spanner/docs/schema-and-data-model#creating_a_hierarchy_of_interleaved_tables https://cloud.google.com/spanner/docs/schema-and-data-model#...