score:9

Accepted answer
from t in (
           from h in accountquery
           join u in ubuquery on h.compoundkey1.ucet equals u.ucet
           select new {h,u}
           ) group t by new {t.h.compoundkey1.ucet} into g 

            select new {
                    ucet = g.key.ucet,
                    md = g.sum(k => k.h.md),
                    dal = g.sum(k => k.h.dal),
                    md_m = g.sum(k => k.h.mdm),
                    dal_m = g.sum(k => k.h.dalm),
                    kod = g.max(k => k.u.kod)  
                };

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