table  - a . it has 3 fields named region,month,customers


region month customers
1      1     10
1      2     9
1      3     5 
2      1     8
2      2     3
3      1     2

for region 1 i have 10 customers

lets my problem is
i have 0 customers for region 2 in month 3

now i want to show that for region 2 - month =3 and value = 0

hoe to make it
pls tell