text: Create table If Not Exists Activity (machine_id int, process_id int, activity_type ENUM('start', 'end'), timestamp float);
  Truncate table Activity;
  insert into Activity (machine_id, process_id, activity_type, timestamp) values ('0', '0', 'start', '0.712');
  insert into Activity (machine_id, process_id, activity_type, timestamp) values ('0', '0', 'end', '1.52');
  insert into Activity (machine_id, process_id, activity_type, timestamp) values ('0', '1', 'start', '3.14');
  insert into Activity (machine_id, process_id, activity_type, timestamp) values ('0', '1', 'end', '4.12');
  insert into Activity (machine_id, process_id, activity_type, timestamp) values ('1', '0', 'start', '0.55');
  insert into Activity (machine_id, process_id, activity_type, timestamp) values ('1', '0', 'end', '1.55');
  insert into Activity (machine_id, process_id, activity_type, timestamp) values ('1', '1', 'start', '0.43');
  insert into Activity (machine_id, process_id, activity_type, timestamp) values ('1', '1', 'end', '1.42');
  insert into Activity (machine_id, process_id, activity_type, timestamp) values ('2', '0', 'start', '4.1');
  insert into Activity (machine_id, process_id, activity_type, timestamp) values ('2', '0', 'end', '4.512');
  insert into Activity (machine_id, process_id, activity_type, timestamp) values ('2', '1', 'start', '2.5');
  insert into Activity (machine_id, process_id, activity_type, timestamp) values ('2', '1', 'end', '5');
  