alter table tfi add constaint mass_check check (
case when tfi.mass2 is null then 0 else tfi.mass2 end+
case when tfi.mgon is null then 0 else tfi.mgon end+
case when tfi.mpkom is null then 0 else tfi.mpkom end+
case when tfi.mpech is null then 0 else tfi.mpech end>tfi.mass1)