Jeff Janes <jeff.janes@gmail.com> writes:
> Will PG allow you to add a FK constraint where there is no usable
> index on the referenced side?
It will not, because the referenced side must have a unique constraint,
ie an index.
The standard performance gotcha here is not having an index on the
referencing side. But that only hurts when doing UPDATEs/DELETEs of
referenced-side keys, which as far as I gathered was not the OP's
scenario.
regards, tom lane
