Access nested select in field listing - sql

Question

I have been provided a query to search for some data in the db that looks like this:
select nvl(to_char(a.empresa), 'SEM REMESSA') empresa,
c.conta,
nvl(sum(a.valor_total), 0) as folha,
(select count(distinct(l2.creditado))
from lancamentos l2
inner join vw_arquivos a2
on l2.arquivo = a2.arquivo
where a2.empresa = a.empresa) as funcionarios
from conta_table c
left join vw_arquivos a
on c.conta = a.conta
and a.situacao = 6
group by a.empresa, c.conta
I have to get the value of the operation folha / funcionarios, but if I put this in the field listing I get the error:
ORA-00904: "FUNCIONARIOS": invalid identifier
00904. 00000 - "%s: invalid identifier"
And when I replace my reference to funcionarios with the same nested select, I get the same error on reference folha.
I know I could just replace both references with their respective calculations, and it works. Like this:
nvl(sum(a.valor_total), 0) /
(select count(distinct(l2.creditado))
from lancamentos l2
inner join vw_arquivos a2
on l2.arquivo = a2.arquivo
where a2.empresa = a.empresa) as division
But this looks not so optimized and not like the best way to do it. So my question is...
Is there any way to select these values with this last division operation, but more optimized than repeating the folha and funcionarios calculations? Maybe a way to reference these already calculated values.

Answer 1

folha and funcionarios cannot be referenced in the same query because they are aliases. You have to make the entire query as subquery, and get the division, like so:
select empresa, conta, folha/funcionarios folha_div_funcionarios
from (
select nvl(to_char(a.empresa), 'SEM REMESSA') empresa,
c.conta,
nvl(sum(a.valor_total), 0) as folha,
(select count(distinct(l2.creditado))
from lancamentos l2
inner join vw_arquivos a2
on l2.arquivo = a2.arquivo
where a2.empresa = a.empresa) as funcionarios
from conta_table c
left join vw_arquivos a
on c.conta = a.conta
and a.situacao = 6
group by a.empresa, c.conta
)