|| at Jul 28, 2009 at 9:11 pm
2009/7/28 Tom Lane [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.