Do I need to create indexes on foreign keys on Oracle?

Question

I have a table A and a table B. A has a foreign key to B on B\'s primary key, B_ID.

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Answer 1

As with anything relating to performance, it depends on many factors and there is no silve bullet e.g. in a very high activilty environment the maintainance of an index may be unacceptable.

Most salient here would seem to be selectivity: if the values in the index would be highly duplicated then it may give better performance to drop the index (if possible) and allow a table scan.