SQL simplify coalesce query

Question

I've created the following query:

select k.vname, k.nname, coalesce(
  to_char((
    select a1.ablaufdat
    from kunde k1
    natural join abonnement a1
    where k.vname = k1.vname and k.nname = k1.nname
    and a1.ablaufdat < to_date('01-01-2015', 'DD-MM-YYYY')
))
, '-')
from kunde k
left outer join abonnement a on k.knr = a.knr 
order by k.vname asc, k.nname asc;

It shows me all customers with a subscription which ends before 2015 with the corresponding date or - if there is no corresponding date, which is the intended result.

However, the query is too complicated in my opinion and I couldn't find a simplier way. I would appreciate if you could help me with simplifying it.
Thank you very much.

Answer 1

You say that there can be just one abonnement per kunde. So just outer join and see if you got a record:

select k.knr, k.vname, k.nname,
  coalesce(to_char(a.ablaufdat), '-' ) as ablaufdatum
from kunde k 
left outer join abonnement a on a.knr = k.knr and a.ablaufdat < to_date('01-01-2015', 'DD-MM-YYYY')
order by k.vname asc, k.nname asc;