Help needed in EXPLAIN PLAN for a partitioned table

Question

Oracle Version 9i
(Paste execution plan in a spreadsheet to make sense out of it)
I am trying to tune this query -
select * from comm c ,dates d
where
d.active_period = 'Y'
and c.period = d.period;
Operation     Object Name     Rows     Bytes     Cost     Object Node     In/Out     PStart     PStop
SELECT STATEMENT Optimizer Mode=CHOOSE          5 M          278887                     
HASH JOIN          5 M     5G     278887                     
TABLE ACCESS FULL     SCHEMA.DATES     24      1 K     8                     
PARTITION LIST ALL                                   1     8
TABLE ACCESS FULL     SCHEMA.COMM     6 M     5G     277624                1     8
However, I know that the dates table will return only one record. So, if I add another condition to the above query, I get this execution plan. The comm table is huge but it is partitioned on period.
select * from comm c ,dates d
where
d.active_period = 'Y'
and c.period = qd.period
and c.period = 'OCT-07'
Operation     Object Name     Rows     Bytes     Cost     Object Node     In/Out     PStart     PStop
SELECT STATEMENT Optimizer Mode=CHOOSE          1           8                     
MERGE JOIN CARTESIAN          1      9 K     8                     
TABLE ACCESS FULL     SCHEMA.DATES     1      69      8                     
BUFFER SORT          1      9 K                         
TABLE ACCESS BY LOCAL INDEX ROWID     SCHEMA.COMM     1      9 K                    7     7
INDEX RANGE SCAN     SCHEMA.COMM_NP9     1                          7     7
How can I make the query such that the comm table does not have to traverse all of its partitions? The partitioning is based on quarters so it will get its data in one partition only (in the above example - partition no. 7)
Thanks in advance for writing in your replies :)

Answer 1

You need to specify period = 'OCT-07', otherwise there is no way the optimizer can know it needs to access only one partition.
Alternatively, partition the DATES table in exactly the same way on "period", and partition-wise joins should kick in, and effectively accessing only the active partition.