Best Optimum Solution with Explanation! (Using Joins)
Please Upvote my solution, if you find it helpful ;)\n\n# Intuition\nThe problem asks us to calculate the average time taken to process each machine based on st
## ***Please Upvote my solution, if you find it helpful ;)***\n\n# Intuition\nThe problem asks us to calculate the average time taken to process each machine based on start and end activities recorded in the "Activity" table.\n\n# Approach\nTo solve this problem, we use a SQL query with the following steps:\n\n1. We join the "Activity" table with itself using the "machine_id" column. This allows us to pair the start and end activities for each machine.\n1. We filter the rows to include only the start activities for the first occurrence and the end activities for the second occurrence. This ensures we have matched start and end activities for each machine.\n1. We calculate the time difference between the start and end activities for each machine by subtracting the start timestamp from the end timestamp.\n1. We use the AVG function to calculate the average processing time for each machine.\n1. We round the average processing time to three decimal places using the ROUND function.\n1. Finally, we group the results by "machine_id" to get the average processing time for each machine.\n\n# Complexity\n- Time complexity:\nThe time complexity of this query depends on the size of the "Activity" table and the efficiency of the database engine. For a well-indexed table, the time complexity is usually efficient. We can say that it will take $$O(n log n)$$ or $$O(n)$$ time, where n is the number of rows in the "Activity" table. The database engine uses techniques like indexing and joining algorithms to quickly process the query.\n\n- Space complexity:\nThe space complexity of this query is determined by the size of the result set. In other words, it depends on the number of machines for which there are start and end activities. We can say the space complexity is $$O(n)$$, where n is the number of machines. The memory required to store the result set grows with the number of machines.\n\n# Code\n```\n# Write your MySQL query statement below\nSELECT \n    s.machine_id, \n    ROUND(AVG(e.timestamp-s.timestamp),3) as processing_time \nFROM Activity s\nJOIN Activity e ON e.machine_id=s.machine_id\nWHERE s.activity_type=\'start\' AND e.activity_type=\'end\'\nGROUP BY s.machine_id\n```\n***Please Upvote my solution, if you find it helpful ;)***\n![6a87bc25-d70b-424f-9e60-7da6f345b82a_1673875931.8933976.jpeg](https://assets.leetcode.com/users/images/0e5e5357-5af9-4902-a584-62f5ac275515_1685478393.9930801.jpeg)\n
['Database', 'MySQL']