Re: Foreign keys for non-default datatypes, redux

I wrote:
>> * Add an oid[] column to pg_constraint that stores the equality operator
>> OIDs for a foreign-key constraint, in the same column order as conkey[]
>> and confkey[].

It turns out this isn't sufficient: ri_Check_Pk_Match() wants to
generate PK = PK checks, and the PK = FK operator isn't the right one
for that. The information I suggested adding to pg_constraint isn't
enough to let it find out which operator is the right one.

We could handle this in a couple of ways:

1. Add yet another column with PK=PK operator OIDs to pg_constraint.

2. Add a column with the underlying PK index's OID to pg_constraint, and
expect ri_Check_Pk_Match to dredge the info from that. This is probably
possible, but not exactly trivial because of which-column-is-which
considerations.

3. Leave pg_constraint alone and expect ri_Check_Pk_Match to look in
pg_depend to find out the underlying PK index, then proceed as in #2.

From an efficiency standpoint #1 seems the best, and yet it seems a bit
ugly. Not that the others aren't. Comments, other ideas?

regards, tom lane