2009/7/28 Tom Lane <tgl@sss.pgh.pa.us>:
> [sigh, forgot to cc hackers the first time ]
>
> Foreign key behavior is only sane if the referenced column(s) are
> unique. With the proposed patch, it is possible that the uniqueness
> check on the referenced columns is deferred, which means it might not
> occur till after an FK check does. Discuss.
>
> regards, tom lane
>
Hmm, yes, looking in the SQL spec, I've just noticed this under 11.8,
referential constraint definition:
"The table constraint descriptor describing the <unique constraint
definition> whose <unique column list> identifies the referenced
columns shall indicate that the unique constraint is not deferrable."
which seems like a sensible policy now that I think about it.
- Dean