UPDATE
mylib/svakvb a
set a.kvb34 =
(SELECT b.rank2
from mylib/ranking b where
b.rank1 = a.kvb02 and
a.kvb01 = '01' and
a.kvb34 <> b.rank2 )
where b.rank1 = a.kvb02 and
a.kvb01 = '01' and
a.kvb34 <> b.rank2