"Ehab Galal" <ehabgalal123@hotmail.com> writes:
> If i understand correctly, i may use systable_beginscan() and
> systable_getnext() to scan a system table while specifying a key (e.g.,
> username='user1'). But i know nothing about specifying the order of the
> scan.
The systable_xxx functions allow implementation by either indexscan or
seqscan, therefore they guarantee *nothing* about retrieval order.
If your code does not need to be executed during bootstrap or crash
recovery, you could depend on an indexscan instead. See
toast_fetch_datum() for an example.
regards, tom lane