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LeetCode

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Problem

Table: RequestAccepted

+----------------+---------+
| Column Name    | Type    |
+----------------+---------+
| requester_id   | int     |
| accepter_id    | int     |
| accept_date    | date    |
+----------------+---------+
(requester_id, accepter_id) is the primary key for this table.
This table contains the ID of the user who sent the request, the ID of the user who received the request, and the date when the request was accepted.

Write an SQL query to find the people who have the most friends and the most friends number.

The test cases are generated so that only one person has the most friends.

The query result format is in the following example.

Example 1:

Input: 
RequestAccepted table:
+--------------+-------------+-------------+
| requester_id | accepter_id | accept_date |
+--------------+-------------+-------------+
| 1            | 2           | 2016/06/03  |
| 1            | 3           | 2016/06/08  |
| 2            | 3           | 2016/06/08  |
| 3            | 4           | 2016/06/09  |
+--------------+-------------+-------------+
Output: 
+----+-----+
| id | num |
+----+-----+
| 3  | 3   |
+----+-----+
Explanation: 
The person with id 3 is a friend of people 1, 2, and 4, so he has three friends in total, which is the most number than any others.

Code

select id1 as id, count(id2) as num
from
(select requester_id as id1, accepter_id as id2 
from RequestAccepted
union
select accepter_id as id1, requester_id as id2 
from RequestAccepted) tmp1
group by id1 
order by num desc limit 1