item  qty
--------
3001   1
3003   3
3004   1
3006   2

item   qty
----------
3001    2
3002    3
3006    3
3008    6

item    qty
-----------
3001     3
3002     3
3003     3
3004     1
3006     5
3008     6

SELECT Item, SUM(qty) as Qty FROM
(
   SELECT Item, qty FROM warehouse_1
   UNION
   SELECT Item, qty FROM warehouse_2
) as a
GROUP BY item;

select item,sum(qty) from(
select item, Qty from warehouse_1 UNION
select item, Qty from warehouse_2
)x group by item

CREATE OR REPLACE VIEW warehouse_3 as
    SELECT coalesce(w1.item,w2.item) as item, w1.qty+w2.qty as qty
    FROM warehouse_1 as w1
    OUTER JOIN warehouse_2 as w2
    ON w1.item = w2.item;

select * from warehouse_3;

SELECT item , SUM(qty)
FROM (
   SELECT item, qty
   FROM warehouse_1
   UNION
   SELECT item, qty
   FROM warehouse_2
) AS U GROUP BY item

create table tbl1(item int,qty int)
INSERT INTO tbl1
VALUES(3001,1),(3003,3),(3004,1),(3006,2)

create table tbl2(item int,qty int)
INSERT INTO tbl2
VALUES(3001,2),(3002,3),(3006,3),(3008,6)


select isnull(t1.item,t2.item) as item,isnull(t1.qty,0)+isnull(t2.qty,0) as qty from tbl1 t1 full outer join tbl2 t2 on t1.item =t2.item
order by 1