"wangshj" <wangshj@sduept.com> writes:
> Description: System column oid is not unique

There isn't, and never has been nor will be, any promise that it is,
except to the extent that uniqueness is enforced by a unique index
on a particular table. OID is just a kind of serial sequence generator.

regards, tom lane

---------------------------(end of broadcast)---------------------------
TIP 9: In versions below 8.0, the planner will ignore your desire to
choose an index scan if your joining column's datatypes do not
match