Can anyone help me with this exercise ?:
 Show for each contract the total amount of commissions, amount payable, amount paid.
The tables that are named in it are:
Contracts: dni, cuit, nro_contract, cod_cargo, salary, percentage_comision, date_incorporation, date_finalization_contract, expiration date, application_date
Commissions: anio_contrato, month_contract, nro_contract, import_commission, payment_date
And what I try to do partially is:
select nro_contrato as 'NUMERO CONTRATO',
count(*) as 'CANTIDAD TOTAL DE COMISIONES', *************
from comisiones
group by 1;
But I can not understand how to make part of the paid and to pay.
Pd: The ************* is where I can not think of what to put.

If it has already been paid, it has a date and if it is not going to be invalid the value of payment_date

The amount to pay implies the number of commissions that still have to be paid (that is, if there are 4 commissions that have to be paid within a month, it means that there are 4 'amounts to be paid') and the amounts paid are the number of commissions that have already been paid (if there are 3 commissions that were paid yesterday, it means that there are 3 'amounts paid')