코딩테스트 SQL 코드카타 (Average Time of Process per Machine)

문제

Average Time of Process per Machine - LeetCode

 

There is a factory website that has several machines each running the same number of processes.
Write a solution 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 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

 

 

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풀이

1. activity_type 나누기
2. 시간 계산하기 (end - start)
3. 평균 구하기

 

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코드

with로 공통의 테이블을 정의한다.

a1은 start를 a2 는 end로 설정하고 각각을 하나의 테이블에 불러와서 호출한다.

 

이를 불러와 avg로 평균을 계산한다.

이때 소수점 3자리니 round ( _, 3) 해야한다.

 

machine별로 정의하니, machine_id로 그룹화한다.

with duration as (
    select a1.machine_id, a1.process_id, (a2.timestamp - a1.timestamp) as time
    from Activity a1
    join Activity a2
    on a1.machine_id = a2.machine_id
    where a1.activity_type = "start" and a2.activity_type = "end"
)
select machine_id, round(avg(time),3) as processing_time
from duration
group by machine_id

 

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링크

LeetCode/1661-average-time-of-process-per-machine at main · K-MarkLee/LeetCode

LeetCode/1661-average-time-of-process-per-machine at main · K-MarkLee/LeetCode