[SQL/코드카타] Average Time of Process per Machine

문제Table: Activity더보기+----------------+---------+| Column Name | Type |+----------------+---------+| machine_id | int || process_id | int || activity_type | enum || timestamp | float |+----------------+---------+The table shows the user activities for a factory website.(machine_id, process_id, activity_type) is the primary key (combination of columns with unique v..