https://github.com/manojvermadatabase/sql_interview
PRACTICE SET FOR INTERVIEW
https://github.com/manojvermadatabase/sql_interview
sql-server
Last synced: 8 months ago
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PRACTICE SET FOR INTERVIEW
- Host: GitHub
- URL: https://github.com/manojvermadatabase/sql_interview
- Owner: manojvermadatabase
- Created: 2025-04-18T08:24:04.000Z (9 months ago)
- Default Branch: main
- Last Pushed: 2025-04-30T17:40:19.000Z (9 months ago)
- Last Synced: 2025-04-30T18:39:28.298Z (9 months ago)
- Topics: sql-server
- Homepage:
- Size: 22.5 KB
- Stars: 2
- Watchers: 1
- Forks: 0
- Open Issues: 0
-
Metadata Files:
- Readme: README.md
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README
The SQL Developer Interview Guide is a comprehensive resource designed to help candidates prepare for interviews related to SQL development roles. It covers essential topics such as SQL queries, database design, normalization, indexing, stored procedures, performance tuning, and real-world problem-solving scenarios. This guide also includes frequently asked interview questions, best practices, and tips to showcase your SQL skills confidently. Whether you're a beginner or an experienced developer, this guide equips you with the knowledge and strategies to succeed in your next interview.
## //Average Time of Process per Machine//
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 (combination of columns with unique values) 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 (category) 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.
It is guaranteed that each (machine_id, process_id) pair has a 'start' and 'end' timestamp.
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
## SOLUTION OF Average Time of Process per Machine
```sql
SELECT
machine_id,
ROUND(AVG(end_time - start_time), 3) AS processing_time
FROM (
SELECT
a.machine_id,
a.process_id,
MAX(CASE WHEN a.activity_type = 'start' THEN a.timestamp END) AS start_time,
MAX(CASE WHEN a.activity_type = 'end' THEN a.timestamp END) AS end_time
FROM
Activity a
GROUP BY
a.machine_id, a.process_id
) AS subquery
GROUP BY
machine_id;
```