We ran into this problem with some of our code. When our DBA talked with Oracle Tech Support, they said to use an index hint. The Oracle tech said that an index would then be used, unless the parameter started with wildcard. At that time it would recompile the query to not use the index. Oracle would then keep both versions of the query cached and would use the appropriate one. The hints are just that, hints. If it doesn't work then Oracle ignores them.