> > Af far as I know Oracle doesn't have any short cut (along the lines of
> > what is being discussed in this thread) for this operation. However
> > Oracle is more efficient in providing the answer than postgres
> currently
> > is. While postgres needs to perform a full scan on the table, Oracle
> > will only need to perform a full index scan on the primary key if one
> > exists. Since the index will likely have much less data than the full
>
> Under Postgres, a full index scan is generally more expensive than a full
> table scan since indices, particularly btree, carry a large amount of meta
> data and theefore consume more pages.
Don't forget that Postgres also doesn't store tids in the index, so must
always check with the main table that a row is visible in current
transaction.
Chris