Query SQL to subtract two fields

Question

My query is that I have two tables, one called sec_users with the following fields:

pk_user, name, dias_disponibles

And anothe

Answer 1

The user1 creates another request for 2 days of sick leave, those 2 days of sick leave do not count as requested days. How can I show those two days requested, using the following code:

SELECT u.pk_user, u.dias_disponibles - sum(s.n_diassolicitados) AS dias_libres 
FROM   sec_users u
LEFT JOIN solicitud s 
on s.fk_empleado = u.pk_user
GROUP BY u.pk_user