Top Travellers

Problem Statement

Table: Users

+---------------+---------+ | Column Name | Type | +---------------+---------+ | id | int | | name | varchar | +---------------+---------+ id is the column with unique values for this table. name is the name of the user.

Table: Rides

+---------------+---------+ | Column Name | Type | +---------------+---------+ | id | int | | user_id | int | | distance | int | +---------------+---------+ id is the column with unique values for this table. user_id is the id of the user who traveled the distance "distance".

Write a solution to report the distance traveled by each user.

Return the result table ordered by travelled_distance in descending order, if two or more users traveled the same distance, order them by their name in ascending order.

The result format is in the following example.

Example 1:

Input: 
Users table:
+------+-----------+
| id   | name      |
+------+-----------+
| 1    | Alice     |
| 2    | Bob       |
| 3    | Alex      |
| 4    | Donald    |
| 7    | Lee       |
| 13   | Jonathan  |
| 19   | Elvis     |
+------+-----------+
Rides table:
+------+----------+----------+
| id   | user_id  | distance |
+------+----------+----------+
| 1    | 1        | 120      |
| 2    | 2        | 317      |
| 3    | 3        | 222      |
| 4    | 7        | 100      |
| 5    | 13       | 312      |
| 6    | 19       | 50       |
| 7    | 7        | 120      |
| 8    | 19       | 400      |
| 9    | 7        | 230      |
+------+----------+----------+
Output: 
+----------+--------------------+
| name     | travelled_distance |
+----------+--------------------+
| Elvis    | 450                |
| Lee      | 450                |
| Bob      | 317                |
| Jonathan | 312                |
| Alex     | 222                |
| Alice    | 120                |
| Donald   | 0                  |
+----------+--------------------+
Explanation: 
Elvis and Lee traveled 450 miles, Elvis is the top traveler as his name is alphabetically smaller than Lee.
Bob, Jonathan, Alex, and Alice have only one ride and we just order them by the total distances of the ride.
Donald did not have any rides, the distance traveled by him is 0.

Solutions

Approach

we will apply left join on id = user_Id and then group by userId and it will sum will add all the grouped distance and return it and if the value is null then ifull will return 0 and atlast we will order them.

Sql

SELECT u.name, IFNULL(SUM(r.distance), 0) AS travelled_distance
FROM Users u
LEFT JOIN Rides r
ON u.id = r.user_id
GROUP BY r.user_id
ORDER BY travelled_distance DESC, u.name ASC;

Pandas

import pandas as pd

def top_travellers(users: pd.DataFrame, rides: pd.DataFrame) -> pd.DataFrame:
    
    df = rides.groupby( ['user_id'])['distance'].sum().reset_index(name='travelled_distance' )

    df = pd.merge( users, df, how='left', left_on='id', right_on='user_id')

    df['travelled_distance'] = df['travelled_distance'].fillna(0)

    df.sort_values( by=['travelled_distance','name'], ascending=[False,True], inplace=True )

    return df[['name','travelled_distance']]