how to filter date type column ?

[lk_phoenix]

hi,all:
I have a table with a column as date type, I try to use it as a where 
condition: but it was not work.

select date,TO_DATE('2015-06-01','yyyy-MM-dd') 
,date=TO_DATE('2015-06-01','yyyy-MM-dd')from FARM_PRODUCT_PRICE limit 100;



and ,I can do it like this : 
select * from FARM_PRODUCT_PRICE where TO_CHAR(date, 'yyyy-MM-dd') = 
'2016-09-29' ;
but , it will not use index if I create index like this :
CREATE INDEX idx_fpp ON FARM_PRODUCT_PRICE (TO_CHAR(date, 'yyyy-MM-dd'));




thanks for any help.

2016-12-02


lk_phoenix