I get error: `ORA-00907: missing right parenthesis`, but i can't find the wrong stuff.

```
(select listagg(sp.name
||' : '||
(case when count(distinct sp.name) < 1 then NULL else szf.piece END) as cou_1, ',') 
WITHIN GROUP (ORDER BY sp.name,cou_1)
from sk_positions sp, sk_stock_f SZF, sk_stock SZ 
where SZF.CODE_ID =SK.ID AND SP.RID = SZF.RID_U AND SZF.ID_SZ = SZ.ID
and sp.sk_u = (%sk%) and SZF.piece != 0)

```

I think, i have problem in `listagg - case`.