Different Result Same Sql Queries

I wrote 2 sql queries in two different ways.
The only difference in both queries are One using '=' and other one using 'in'.
All the other data is same.In my sense '=' and 'in' same
Both queries should give same result.
But one query giving different result and other query giving different result.
Is this 2 queries different??


SELECT sum(SALES_ITEM.NET_PRICE)
FROM PRODUCT_GROUP_LINK,
PRODUCT,
SALES_ITEM
WHERE (PRODUCT_GROUP_LINK.PRODUCT_CODE=PRODUCT.PRODUCT_CODE)
AND (PRODUCT_GROUP_LINK.PRODUCT_CODE=SALES_ITEM.ORIG_PRODUCT)
AND PRODUCT.STYLE_CODE='MC001'
AND (SALES_ITEM.PRICE_LIST='1FAC'
OR SALES_ITEM.PRICE_LIST='1FAW' )
AND CLASS_CODE='TYPE'
group by STYLE_CODE


SELECT sum(sales_item.net_price)
from PRODUCT,
product_group_link,
SALES_ITEM
WHERE (PRODUCT_GROUP_LINK.PRODUCT_CODE=PRODUCT.PRODUCT_CODE)
AND (PRODUCT_GROUP_LINK.PRODUCT_CODE=SALES_ITEM.ORIG_PRODUCT)
AND PRODUCT.STYLE_CODE='MC001'
AND sales_item.PRICE_LIST IN ('1FAC','1FAW')
AND CLASS_CODE='TYPE'
group by style_code

Any idea?
Thanks