SQL Interview Questions – Average Time of Process per Machine

Problem Description –

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.

Problem Link – Average Time

Difficulty Level – Easy

Solution –

SELECT
    machine_id,
    ROUND((SUM(CASE WHEN activity_type = 'end' THEN timestamp END) - SUM(CASE WHEN activity_type = 'start' THEN timestamp END)) / (SELECT COUNT(DISTINCT process_id) FROM Activity),3) as processing_time
FROM Activity
GROUP BY 1
ORDER BY 1