I have worked on the Zabbix data analyzer, where I had to get history data per day. I have tried to use Zabbix API ("history.get" method) and it's just doesn't worked. Rather, I was able to got history data per hour and nothing else. But I got data per day via SQL query and it was OK, when "history.get" method with "time_till" and "time_from" parameters setted for last day was returning NULL every time, when I tried to use it. Of course, this is related to the number of records in the history table (21,684,257), but the SQL query works correctly.