SQL View for Items not sold last six months
Is this what you're looking for?

DECLARE @ItemMaster TABLE (ItemNo INT)
DECLARE @SalesDataMart TABLE (ItemId INT,TranDate DATE)

insert into @ItemMaster (ItemNO) values (1)
insert into @ItemMaster (ItemNO) values (2)

insert into @SalesDataMart (ItemId, TranDate) values (1,'2017-02-17')
insert into @SalesDataMart (ItemId, TranDate) values (2,'2016-02-17')
SELECT *
FROM @ItemMaster itmmst
WHERE NOT EXISTS (
        SELECT *
        FROM @SalesDataMart
        WHERE itemid = itmmst.itemno
            AND Trandate &gt;= Dateadd(month, - 6, sysdatetime())
        )