Now that there are index only scans, there is a use case for having a
composite index which has the primary key or a unique key as the
prefix column(s) but with extra columns after that. Currently you
would also need another index with exactly the primary/unique key,
which seems like a waste of storage and maintenance.
Should there be a way to declare a "unique" index with the unique
property applying to a prefix of the indexed columns/expression? And
having that, a way to turn that prefix into a primary key constraint?
Of course this is easier said then done, but is there some reason for
it not to be a to-do item?
Thanks,
Jeff