easy
\n\n# Code\n\nSELECT a.machine_id,                                              \n       ROUND(AVG(b.timestamp - a.timestamp), 3) as processing_time \nFROM Acti
\n\n# Code\n```\nSELECT a.machine_id,                                              \n       ROUND(AVG(b.timestamp - a.timestamp), 3) as processing_time \nFROM Activity a, activity b                                        \nWHERE a.activity_type = \'start\'                                   \nAND b.activity_type = \'end\'                                       \nAND a.process_id = b.process_id                                   \nAND a.machine_id = b.machine_id                                    \nGROUP BY a.machine_id                                              \n```
['MySQL']