Created an index on a table as
create index IDX on table ( C1||C2||C3||C4)
when i query as follows , in all cases Oracle Performs
FULL TABLE SCAN.
1 select C10 from table where (C1||C2||C3||C4)='xxxxx' OR
2 select /*+ index hint */ C10 from table where (C1||C2||C3||C4)='xxxxx' OR
3 select C10 from table where C1||C2||C3||C4='xxxxx'
4 select C10 from table where ='xxxxx'
PLNOTE: STATS COLLECTED FOR THE INDEX USING DBMS_STATS pkg. And
GRANTED QUERY REWRITE TO THE USER,
ALTER SESSION QUERY_REWRITE_ENABLED =TRUE ,
is already done before the above query is fired.
Could you please help me why its going for FULL TABLE SCAN.

** If am using query as stated in step 3 , does Function based index concept comes here?


Thanx
Sanjay