Getting an error message when one of the values in a formula is null

Question

Hi,
I am using a query to generate report... my query looks like this:
select     
CUSTOMER_NAME,
(sum(MILLAGE)*MILEAGE_RATE) as TOTAL_INVOICE,
from     
     T_TIME_REPORTING
where
CUSTOMER_NAME = :P22_CUST_NAME
group by
CUSTOMER_NAME
it's working fine when there is a valid value for MILLAGE and MILEAGE_RATE but giving an error message when anyone of them is null... please advice how to fix this issue
Thanks in advance

Answer 1

my query looks like this:
select
CUSTOMER_NAME,
(sum(MILLAGE)*MILEAGE_RATE) as TOTAL_INVOICE,
from
T_TIME_REPORTING
where
CUSTOMER_NAME = :P22_CUST_NAME
group by
CUSTOMER_NAMEThat would not work even when all values are not null:
select ename, sum (sal) * comm
    from emp
   where ename = 'ALLEN'
group by ename
Error at line 1
ORA-00979: not a GROUP BY expression