EASY MYSQL SOLUTION
\n\n# Approach\n Describe your approach to solving the problem. \nYou are performing a self-join on the Activity table using the aliases "a" and "b" to join bas
\n\n# Approach\n<!-- Describe your approach to solving the problem. -->\nYou are performing a self-join on the Activity table using the aliases "a" and "b" to join based on machine_id and process_id.\n\nYou use the condition "b.activity_type = \'end\' AND a.activity_type = \'start\'" in the WHERE clause to ensure that you are only considering pairs where the \'start\' activity comes before the \'end\' activity for each (machine_id, process_id) pair.\n\nNext, you GROUP BY a.machine_id to group the results by machine_id.\n\nInside the SELECT statement, you calculate the average processing time for each machine using "AVG(b.timestamp - a.timestamp)" and round the result to 3 decimal places using the ROUND function.\n\n# Code\n```\nSelect a.machine_id , ROUND(AVG(b.timestamp-a.timestamp),3) AS processing_time \nFROM Activity AS a JOIN Activity AS b ON\na.machine_id = b.machine_id AND\na.process_id = b.process_id WHERE\nb.activity_type = \'end\' AND A.activity_type =\'start\' \nGROUP BY a.machine_id;\n\n```
['Database', 'MySQL']