How to Create Function Based Index

Here is an example of creating function based index setting null values to default values:

CREATE INDEX ERKAN.MYTABLE_FUNC_IX on ERKAN.MYTABLE (COL1, COL2,nvl(COL3,COL1), nvl(COL4,to_date('01/01/2009 00:00:00','DD/MM/YYYY hh24:mi:ss')), nvl(COL5,0))
tablespace MYTABLESPACE;