--smazani 0 dif z posledniho datumu
select t.systemvalidsince, count(*) from report t where dif_date = 0  and
                              dif_km = 0 and
                              dif_price = 0 and
                              dif_tech = 0 and
                              dif_desc = 0 and
                              dif_eqpm = 0 and
                              dif_sllr = 0 and
                              dif_extr = 0 group by t.systemvalidsince;
--delete from report t where dif_date = 0  and
                              dif_km = 0 and
                              dif_price = 0 and
                              dif_tech = 0 and
                              dif_desc = 0 and
                              dif_eqpm = 0 and
                              dif_sllr = 0 and
                              dif_extr = 0 ;