RE: Composite indices and skip scanning

As always the choice between using a skip scan or FTS is a CBO decision and
will largely depend on the nature of the object statistics and the SQL.


-----Original Message-----
From: oracle-l-bounce@xxxxxxxxxxxxx
[mailto:oracle-l-bounce@xxxxxxxxxxxxx]On Behalf Of Boyle, Christopher J.
Sent: Thursday, April 15, 2004 9:11 AM
To: oracle-l@xxxxxxxxxxxxx
Subject: Composite indices and skip scanning


Oracle 9.2.0.2.0=20

I have an intersection table composed of PK_TABLE_A, PK_TABLE_B which is
being used to handle a M:M relationship between A and B.  There is a
unique constraint on the combination of the two entries and a
corresponding index with A as the leading value.  When I was trying to
access table A using the PK from table B I expected it to use that index
because of the 9i skip scan feature that allows for a non leading index
member to still utilize the index.  What I got was a FTS until I added a
separate index on PK_TABLE_B only.  Is there something with a unique
index that prevents skip scanning? Or do I have too much blood in my
caffeine and am mis-rembering how the indices should work?

Thanks,
Chris =20

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