Hi,
I stumbled across a few places that depend on the inheritance appends being applied at a later date, so I quickly abandoned that idea. I thought a bit about the indexlist, in particular the inhparent, and I am not sure what depends on get_relation_info working in that way.
Therefore I propose a new attribute partIndexlist of RelOptInfo to include information about uniqueness, in the case the executor can't use the structure that causes the uniqueness to begin with. Said attribute can be used by relation_has_unique_index_for and rel_supports_distinctness.
The attached patch takes that route. I'd appreciate feedback!
Regards
Arne