weirdan

В зависимости от объема выборки, может иметь смысл сделать через временную таблицу с unique index:

create temporary table tablename_uniq like tablename;
alter table tablename_uniq 
  add column record_date date, 
  add unique index (object_id, record_date);
insert ignore into tablename_uniq 
  select id, object_id, time, type_event, cast(time as date) 
  from tablename 
  /* where time between @range_start and @range_end */ 
  order by time desc;
select id, object_id, time, type_event from tablename_uniq;
drop temporary table tablename_uniq;