leetcode - 1661. Average Time of Process per Machine

난이도 : Easy

 

Table: Activity

+----------------+---------+
| 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 of this table.
machine_id is the ID of a machine.
process_id is the ID of a process running on the machine with ID machine_id.
activity_type is an ENUM of type ('start', 'end').
timestamp is a float representing the current time in seconds.
'start' means the machine starts the process at the given timestamp and 'end' means the machine ends the process at the given timestamp.
The 'start' timestamp will always be before the 'end' timestamp for every (machine_id, process_id) pair.

 

There is a factory website that has several machines each running the same number of processes. Write an SQL query to find the average time each machine takes to complete a process.

The time to complete a process is the 'end' timestamp minus the 'start' timestamp. The average time is calculated by the total time to complete every process on the machine divided by the number of processes that were run.

The resulting table should have the machine_id along with the average time as processing_time, which should be rounded to 3 decimal places.

Return the result table in any order.

The query result format is in the following example.

 

Example 1:

Input: 
Activity table:
+------------+------------+---------------+-----------+
| machine_id | process_id | activity_type | timestamp |
+------------+------------+---------------+-----------+
| 0          | 0          | start         | 0.712     |
| 0          | 0          | end           | 1.520     |
| 0          | 1          | start         | 3.140     |
| 0          | 1          | end           | 4.120     |
| 1          | 0          | start         | 0.550     |
| 1          | 0          | end           | 1.550     |
| 1          | 1          | start         | 0.430     |
| 1          | 1          | end           | 1.420     |
| 2          | 0          | start         | 4.100     |
| 2          | 0          | end           | 4.512     |
| 2          | 1          | start         | 2.500     |
| 2          | 1          | end           | 5.000     |
+------------+------------+---------------+-----------+
Output: 
+------------+-----------------+
| machine_id | processing_time |
+------------+-----------------+
| 0          | 0.894           |
| 1          | 0.995           |
| 2          | 1.456           |
+------------+-----------------+
Explanation: 
There are 3 machines running 2 processes each.
Machine 0's average time is ((1.520 - 0.712) + (4.120 - 3.140)) / 2 = 0.894
Machine 1's average time is ((1.550 - 0.550) + (1.420 - 0.430)) / 2 = 0.995
Machine 2's average time is ((4.512 - 4.100) + (5.000 - 2.500)) / 2 = 1.456

 

WITH start AS (
               SELECT machine_id
                    , process_id
                    , activity_type
                    , timestamp
               FROM Activity
               WHERE activity_type = 'start'
               )
    ,end AS (
             SELECT machine_id
                  , process_id
                  , activity_type
                  , timestamp
             FROM Activity
             WHERE activity_type = 'end'
             )
    ,step1 AS (
               SELECT start.machine_id
                    , start.process_id
                    , end.timestamp - start.timestamp processing_time
               FROM start
                    JOIN end ON start.machine_id = end.machine_id
                             AND start.process_id = end.process_id
               GROUP BY machine_id, process_id
               )
SELECT machine_id
     , ROUND(AVG(processing_time), 3) processing_time
FROM step1
GROUP BY machine_id

Accepted (78.65%)

 

 

WITH sub AS (
            SELECT machine_id
                 , process_id
                 , MAX(timestamp) end
                 , MIN(timestamp) start
            FROM Activity
            GROUP BY 1, 2
            )
SELECT machine_id
     , ROUND(SUM(end - start) / COUNT(distinct process_id), 3) processing_time
FROM sub
GROUP BY 1

Accepted (87.19%)