where condition optimization

[Srivats Chandrasekaran]

select
a.nb_group_name as nb_group_name,
master.nb_coupon as nb_coupon,
sum(info.value ),
sum(info3.value),
sum(info6.value),
sum(info12.value),
nb_pool_info info,
nb_pool_info info3,
nb_pool_info info6,
nb_pool_info info12,
AGENCY_MASTER.nb_pool_type_master a,
nb_seller_master seller
where
a.nb_group_name = 'FHCI' and
a.nb_pool_type = master.nb_pool_type and
master.nb_pool_number = info.nb_pool_number and
master.nb_seller_code = seller.nb_seller_code and
seller.nb_seller_name <> 'FREDDIE MAC GIANT' and
info.nb_factor_date = '20041201' and info3.nb_factor_date = date_add('20041201', INTERVAL -3 MONTH ) and
info6.nb_factor_date = date_add('20041201', INTERVAL -(3*2) MONTH ) and
info12.nb_factor_date = date_add('20041201', INTERVAL -(3*4) MONTH ) and
info.nb_pool_number = info3.nb_pool_number and
info.nb_pool_number = info6.nb_pool_number and
info.nb_pool_number = info12.nb_pool_number and
info.nb_sched_balance > 0
GROUP BY
a.nb_group_name,
master.nb_coupon

in this query suppose i dont have records corresponding to info12.nb_factor_date i am getting an empty set as the where condition is failing. Is there any way i get the data corresponding to other dates and null for the dates i dont have the values. For example if i dont have values corresponding to info12.nb_factor_date then i should get null only for only those values and not an emply set.