column aliases

Can someone explain this to me? When I use the alias p, should a
reference to pg_language.oid create a new instance of pg_language in the
range table. Seems it does not. Does the standard say the first query
is legal?

---------------------------------------------------------------------------

test=> select * from pg_language p where p.oid = pg_language.oid;
lanname | lanispl | lanpltrusted | lanplcallfoid | lancompiler
----------+---------+--------------+---------------+-------------
internal | f | f | 0 | n/a
C | f | f | 0 | /bin/cc
sql | f | f | 0 | postgres
(3 rows)

test=> select * from pg_language p, pg_language q where p.oid = q.oid;
lanname | lanispl | lanpltrusted | lanplcallfoid | lancompiler | lanname | lanispl | lanpltrusted | lanplcallfoid | lancompiler
----------+---------+--------------+---------------+-------------+----------+---------+--------------+---------------+-------------
internal | f | f | 0 | n/a | internal | f | f | 0 | n/a
C | f | f | 0 | /bin/cc | C | f | f | 0 | /bin/cc
sql | f | f | 0 | postgres | sql | f | f | 0 | postgres
(3 rows)

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Bruce Momjian | http://www.op.net/~candle
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