Select from Select Drops Connection

Question

I am at a lost what I am doing wrong.
When running this query it works fine ;-
select a.invno, nvl(a.invamt,0) invamt, (select nvl(sum(payment),0) from inv_payment b
where b.invno = a.invo) payment from inv_table a);
Now I try to get those which invoice total does not match payment so I do this ;-
select invno, invamt, payment from (
select a.invno, nvl(a.invamt,0) invamt, (select nvl(sum(payment),0) from inv_payment b
where b.invno = a.invo) payment from inv_table a)
where invamt <> payment;
Upon running the second select statement, sqlplus gives me end-of-communication-channel error and I have to restart sqlplus to connect again.
Can anyone highlight where my mistake is?

Answer 1

I don't have any good idea about why your query would cause an "end of communication" exception, but this query is a bit simpler and should accomplish the same thing.
SELECT *
  FROM (
SELECT it.invno,
       NVL(it.invamt, 0) AS invamt,
       SUM(nvl(ip.payment, 0)) AS payment
  FROM inv_table  it,
       inv_payment  ip
WHERE ip.invno(+) = it.invno
GROUP BY
       it.invno,
       it.invamt
WHERE payment != invamt;