Description
Is your feature request related to a problem or challenge?
A lack documentation on table constraint enforcement makes it difficult for TableProvider authors to have a clear view on when or how TableConstraints might or might not be enforced.
Describe the solution you'd like
Currently there's no good documentation on how DataFusion handles (or rather, doesn't handle) table constraints like primary key, foreign key, or uniqueness. I think it'd be a good idea do have documentation on what DataFusion does or does not enforce (i.e., nullness is enforced, but not uniqueness) as well as hopefully adding common suggestions on how various storage engines have implemented constraints.
I think it'd also likely be useful to have other background like this comment that mention how constraints aren't considered in optimizations while something like distinct count is. The subtle point is that folks might assume that telling datafusion something is a primary key or unique doesn't necessarily mean the optimizer will trust that.
Describe alternatives you've considered
No response
Additional context
No response