SQL & PL/SQL :: ITEM Not In CURR_STS Table Not To Be Displayed

CREATE TABLE CURR_STS
(
LOB VARCHAR2(100 CHAR),
FP VARCHAR2(100 CHAR),
BRAND VARCHAR2(100 CHAR),
ITEM VARCHAR2(100 CHAR),
SUB_ITEM VARCHAR2(100 CHAR),
PART VARCHAR2(100 CHAR),
COST NUMBER
[code]...

ITEM not in CURR_STS table not to be displayed ( HERE SKU2) , but SUB_ITEM, PART coming under a ITEM if present in SAME ITEM in CURR_STS ( here SKU1 is common in both CURR_STS and PRIOR_STS) to be displayed. Trying to achieve this through OUTER join queries.

SELECT a.lob,a.sku,a.mod,a.part,a.cost curr_cost, b.cost prior_cost
FROM curr_sts a, prior_sts b
WHERE a.item=b.item(+) and a.sub_item=b.sub_item(+) and a.part=b.part(+);