Código SQL [-] Update t1 set c1 = (select case t1 when 1 then c2 when 2 then c3 when 3 then c4 else c5 end from t2 where condicion)
Update t1 set c1 = (select case t1 when 1 then c2 when 2 then c3 when 3 then c4 else c5 end from t2 where condicion)