Regarding index usage

[Ramesh R G V S]

Hi all
I have a table with an index.Under what conditions the sqls will not be able to use the index.
The cases which i found are like
1.If the column that is indexed is modified in the where part then index will not be used for the statement.The modification is either using the indexed column in an expression like
COL1 || ' ' like 'A%'
or with a function around the indexed column like
NVL(COL1,' ')...
Is there any other situations where a statement did not use index.
Regards
Ramesh R G V S