How do I...how we can calculate the difference of sum of two tables....

; with table1grouped as (
    SELECT ItemName,Sum(Quantity) as Quantity
    FROM table1
    GROUP BY itemName
), table2grouped as (
    SELECT ItemName,Sum(Quantity) as Quantity
    FROM table2
    GROUP BY itemName
)
SELECT ItemName, (t1g.Quantity - ISNULL(t2g.Quantity,0)) as Quantity
FROM table1grouped t1g
LEFT JOIN table2grouped t2g on t1g.ItemName = t2g.ItemName

select  sub.ItemName, SUM(sub.Quatity) from (select Table1.ItemName ,SUM(Table1.Quantity)Quatity from Table1
group by  Table1.ItemName
union
select Table2.ItemName ,SUM(Table2.Quantity)*-1 Quatity from Table2
group by  Table2.ItemName) sub group by ItemName

CREATE PROC PR_TEST_PROC
AS
BEGIN
 

CREATE TABLE #tmp_TBL1
(
itemName varchar(100),
Qty int
)
 
INSERT INTO #tmp_TBL1
SELECT ItemName,Sum(Quantity)
FROM table1
group by itemName
 
--Uncomment below if you want to check output of table
--SELECT * from #tmp_TBL1

CREATE TABLE #tmp_TBL2
(
itemName varchar(100),
Qty int
)
 
INSERT INTO #tmp_TBL2
SELECT ItemName,Sum(Quantity)
FROM table2
group by itemName
 
--Uncomment below if you want to check output of table
--SELECT * from #tmp_TBL2

 

--mentioned alias--
SELECT t1.ItemName, t1.Qty - t2.Qty as Qty
from #tmp_TBL1 t1,#tmp_TBL2 t2
WHERE t1.itemName = t2.ItemName
 

 

 

END