sql for net price calculation needs tuning

Hi:

We are using oracle EBS 12.2.4 with database version 11.2.0.4. We have below sql statement that would like to tune. I have used sql tuning advisor and it has given me the recommendation to remove the cartisean product. However, I am a little bit confused and not sure what it means. Gurus, could you please advise? Thank you.

SELECT Y.*, CATALOG_ELEMENTS.* FROM (

SELECT

X.*,

ROW_NUMBER() OVER (PARTITION BY X.ACCOUNT_NUMBER, X.ITEM_NUMBER ORDER BY X.NET_PRICE ASC) BESTDISC

FROM (

SELECT

T.PRODUCT_ATTR_VALUE,

CATALOG_ITEMS.ITEM_NUMBER,

CATALOG_ITEMS.listprice PUBLISHED_LIST_PRICE,

CASE WHEN T.PRODUCT_ATTRIBUTE_TYPE = 'Item Category' then (T.OPERAND) || '%' else null end PUBLISHED_DIST_PRICE_MULT,