ok

select
c1.spaceid,s.spacekey,s.spacename,sum(cp.longval) as "size (byte)"
from content c1 join content c2 on c1.contentid = c2.pageidjoin contentproperties cp on c2.contentid = cp.contentidjoin spaces s on c1.spaceid=s.spaceidwhere c2.contenttype='ATTACHMENT'
group by c1.spaceid, s.spacekey, s.spacename;