easy solution with explanation.
Intuition\n Describe your first thoughts on how to solve this problem. \n\n# Approach\n\n1. CTE ProcessTimes:\n\n- The MAX(CASE WHEN a.activity_type = \'start\'
# Intuition\n<!-- Describe your first thoughts on how to solve this problem. -->\n\n# Approach\n\n1. CTE ProcessTimes:\n\n- The MAX(CASE WHEN a.activity_type = \'start\' THEN a.timestamp END) extracts the start_time for each (machine_id, process_id) pair.\n- The MAX(CASE WHEN a.activity_type = \'end\' THEN a.timestamp END) extracts the end_time.\n- This CTE groups by machine_id and process_id to calculate the start_time and end_time for each process.\n2. CTE Durations:\n\n- This CTE calculates the duration for each process by subtracting start_time from end_time.\n3. Final Query:\n\n- ROUND(AVG(duration), 3) computes the average duration for each machine_id, rounded to 3 decimal places.\n- GROUP BY machine_id groups the results by machine_id to get the average processing time per machine.\n\n# Code\n```mysql []\n# Write your MySQL query statement below\nWITH ProcessTimes AS (\n    SELECT \n        a.machine_id,\n        a.process_id,\n        MAX(CASE WHEN a.activity_type = \'start\' THEN a.timestamp END) AS start_time,\n        MAX(CASE WHEN a.activity_type = \'end\' THEN a.timestamp END) AS end_time\n    FROM \n        Activity a\n    GROUP BY \n        a.machine_id,\n        a.process_id\n),\nDurations AS (\n    SELECT \n        machine_id,\n        (end_time - start_time) AS duration\n    FROM \n        ProcessTimes\n)\nSELECT \n    machine_id,\n    ROUND(AVG(duration), 3) AS processing_time\nFROM \n    Durations\nGROUP BY \n    machine_id;\n\n```
['MySQL']