Complex query

Hey everybody !!!
I am new on this list !!!

I have a little problem .....

I try this on my system:

"select n_lote from pedidos except select rp.n_lote from relpedidos rp,
relfacturas rf where  rp.n_lote=rf.n_lote group by rp.n_lote having
sum(rp.cantidad)=sum(rf.cantidad)"

I get this result:
ERROR: rewrite: comparision of 2 aggregate
columns not supported 

but if a try this one:

"select rp.n_lote from relpedidos rp, relfacturas rf where 
rp.n_lote=rf.n_lote group by rp.n_lote having sum(rp.cantidad)=sum(rf.cantidad)"

It's OK !!

What's up???
Do you think i found a bug  ???
Do exist some limitation like this in subqueries??

(Perhaps Postgres don't accept using aggregates in subqueries ???)

I tried this too:

"select n_lote from pedidos where n_lote not in (select rp.n_lote from
relpedidos rp, relfacturas rf where  rp.n_lote=rf.n_lote group by rp.n_lote
having sum(rp.cantidad)=sum(rf.cantidad))"

but the result was the same !

And i get the same error message (or similar) when i try other variations.

Thanks !!!

Fer

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