1699 Number of Calls Between Two Persons.md

1699. Number of Calls Between Two Persons

https://leetcode.cn/problems/number-of-calls-between-two-persons/
Table: Calls

Column Name	Type
from_id	int
to_id	int
duration	int

This table does not have a primary key, it may contain duplicates.
This table contains the duration of a phone call between from_id and to_id.
from_id != to_id

Write an SQL query to report the number of calls and the total call duration between each pair of distinct persons (person1, person2) where person1 < person2.

Return the result table in any order.

The query result format is in the following example.

Example 1:
Input:
Calls table:

from_id	to_id	duration
1	2	59
2	1	11
1	3	20
3	4	100
3	4	200
3	4	200
4	3	499

Output:

person1	person2	call_count	total_duration
1	2	2	70
1	3	1	20
3	4	4	999

Explanation:
Users 1 and 2 had 2 calls and the total duration is 70 (59 + 11).
Users 1 and 3 had 1 call and the total duration is 20.
Users 3 and 4 had 4 calls and the total duration is 999 (100 + 200 + 200 + 499).

SELECT
    person1,
    person2,
    COUNT(*) AS call_count,
    SUM(duration) AS total_duration
FROM (
    SELECT
        IF(from_id < to_id, from_id, to_id) AS person1,
        IF(from_id > to_id, from_id, to_id) AS person2,
        duration
    FROM Calls
) p
GROUP BY person1, person2