return modified data from a function

Hi,

We have a table for an account system:

table:
compte

fields:
detail => varchar
deure => float
haver => float

some data:

detail: Entrada
deure: 0
haver: 5000

detail: Sortida
deure: 100
haver: 0

detail: Comptes
deure: 150
haver: 0

detail: Varis
deure: 35
haver: 0

We want to retrieve all this records, with an extra column with the
difference from deure-haver, like this:

Entrada 0 5000 5000
Sortida 100 0 4900
Comptes 150 0 4750
Varis 35 0 4715

We tried using functions, with a cursor, and add an extra column or
tried to create a view, but without success ...

We have a workaround using our frontend, and there we calculate the
difference, but we want to do it from PostgreSQL.

It's easy to do it ?

thanks in advance,

regards,

raimon fernandez
barcelona