Simple mySQL NO JOIN
\nSELECT machine_id, ROUND((SUM(CASE WHEN activity_type = \'end\' THEN timestamp END)-SUM(CASE WHEN activity_type = \'start\' THEN timestamp END))/COUNT(DISTINC
```\nSELECT machine_id, ROUND((SUM(CASE WHEN activity_type = \'end\' THEN timestamp END)-SUM(CASE WHEN activity_type = \'start\' THEN timestamp END))/COUNT(DISTINCT process_id), 3) processing_time\nFROM Activity\nGROUP BY 1\n```
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