Easiest MySQL Solution 🤩 || Easy To Understand
Intuition\nThe purpose of this SQL query is to calculate the processing time of each machine based on the activities listed in a table called Activity. The Acti
# Intuition\nThe purpose of this SQL query is to calculate the processing time of each machine based on the activities listed in a table called Activity. The Activity table appears to contain records of activities performed by devices (such as \'start\' and \'end\').\n\n# Approach\nHere is a breakdown of how the query works.\n\n**Adding yourself**: Adding yourself to the Activity table in question. This is done to match the \'start\' activities (StartActivity) with the corresponding \'end\' activities (EndActivity) based on machine_id and process_id.\n\n**Filtering:** The WHERE clause extracts rows where StartActivity represents the start of the activity (activity_type = \'beginning\') and EndActivity represents the end of the same activity (activity_type = \'end\').\n\n**Calculation:** The query calculates the time for each activity by subtracting the timestamp of the \'start\' activity (StartActivity.timestamp) from the timestamp of the corresponding \'end\' activity (EndActivity.timestamp) and then using the AVG( ) function.\n\n**Group:** Results are grouped by machine_id using GROUP BY 1, where 1 refers to the first column selected (machine_id). This aggregates the results to give an average operating time for each machine.\n\n# Complexity\n- Time complexity: O(N)\n\n# Code\n```\n# Write your MySQL query statement below\nSELECT\n  StartActivity.machine_id,\n  ROUND(\n    AVG(EndActivity.timestamp - StartActivity.timestamp),\n    3\n  ) AS processing_time\nFROM Activity AS StartActivity\nINNER JOIN Activity AS EndActivity\n  USING (machine_id, process_id)\nWHERE\n  StartActivity.activity_type = \'start\'\n  AND EndActivity.activity_type = \'end\'\nGROUP BY 1;\n```\n![upvote.jpeg](https://assets.leetcode.com/users/images/bf45c9d9-f6d8-4e4f-bcab-e4bc0c91b233_1721673607.449458.jpeg)\n\n
['MySQL']