8/25 每日一題(MYSQL 合併表格 列出所有用戶的行駛距離, 距離降序,香同時使用名字升序排列)

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. 

# Write your MySQL query statement below

SELECT Users.name AS name, ifnull(SUM(Rides.distance),0) AS travelled_distance

FROM Users left join Rides on Users.id = Rides.user_id

GROUP BY Users.id

ORDER BY travelled_distance DESC, name

---------------------------

SELECT u.name, SUM(COALESCE(r.distance, 0)) AS travelled_distance FROM users u LEFT JOIN rides r ON r.user_id = u.id GROUP BY u.id ORDER BY travelled_distance DESC, u.name ASC

###COALESCE(null,1) 他會輸出1 , 他會把null轉換成你需要的值

--------------------------

Select u.name,sum(IFNULL(r.distance,0)) as travelled_distance 
from Users u
left join Rides r
on u.id=r.user_id
GROUP BY u.name, u.id
ORDER BY travelled_distance DESC, u.name ASC