Re: Foreign Keys and Indexes

For one, many foreign key columns end up having very low cardinality, and until the bitmapped index was available, you did not want an index on them. You could use the Employee to Dept relationship as an example. If I had many employees, and 2 departments, why would I want a B-Tree index on the Dept columns in the Employee table?
Each foreign key column usage should be looked at to determine if an index is needed.

lolin_at_unexmail.ucdavis.edu wrote in article <854400901.13454_at_dejanews.com>...
> I was surprised to find that when I created a foreign key on a field in a
 child table that access to that table through the key hadn't improved.
>
> Do I have to also create an index on the same field? Why can't Oracle
> use the implied index created for the foreign key? Seems like a waste to
> have to create a "second" index on the same
> field.
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Received on Tue Jan 28 1997 - 00:00:00 CST