Consulta a 3 tablas

[quieropaginaweb]

Gracias por contestar, entonces se quedaría así:

select t1.id_cuenta, sum(t2.importe) as total form tabla_cuenta as t1
inner join tabla_emitidas as t2 on (t1.idcuenta=t2.idcuenta)
group by t1.id_cuenta

UNION

select suma.*, t3.cobros, suma.total-t3.cobros as gran_total from(
select t1.id_cuenta, sum(t2.importe) as total form tabla_cuenta as t1
inner join tabla_emitidas as t2 on (t1.idcuenta=t2.idcuenta)
group by t1.id_cuenta
) as suma
inner join tabla_cobros as t3 on (suma.idcuenta=t3.idcuenta)

Gracias