Query Need to devlelop in sql

Question

I have data with query ,and ouput result ,query is not giving me correct ouput .

 

CREATE TABLE #tbl_Group(B_ID INT,B_Name VARCHAR(50))
CREATE TABLE #tbl_BloodDonor(D_ID INT,D_Name VARCHAR(50),B_ID int,D_QTY int)
CREATE TABLE #tbl_Cross(C_ID INT,D_ID int,C_QTY int,B_ID int )

INSERT INTO #tbl_Group VALUES(1,'A')
INSERT INTO #tbl_Group VALUES(2,'B')
INSERT INTO #tbl_Group VALUES(3,'C')
INSERT INTO #tbl_Group VALUES(4,'D')

INSERT INTO #tbl_BloodDonor VALUES(101,'Hussain',1,1)
INSERT INTO #tbl_BloodDonor VALUES(102,'Akhter',2,1)
INSERT INTO #tbl_BloodDonor VALUES(103,'Ali',3,1)
INSERT INTO #tbl_BloodDonor VALUES(104,'Rehan',2,1)

INsert into #tbl_Cross Values(1,101,1,1)
INsert into #tbl_Cross Values(2,102,1,2)

Select G.B_Name ,Isnull(Isnull(Sum(D.D_QTY),0)-isnull(Sum(C.C_QTY),0),0) Stock
from #tbl_Group G
left outer join #tbl_BloodDonor D on G.B_ID=D.B_ID
left outer join #tbl_Cross c on C.B_ID=G.B_ID
group by G.B_Name

 Output

Group	Stock
A	1
B	0
C	1
D	0