# 1699. Number of Calls Between Two Persons

## Description

Table: Calls

+-------------+---------+
| Column Name | Type    |
+-------------+---------+
| from_id     | int     |
| to_id       | int     |
| duration    | int     |
+-------------+---------+
This table does not have a primary key (column with unique values), it may contain duplicates.
This table contains the duration of a phone call between from_id and to_id.
from_id != to_id


Write a solution 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 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).


## Solutions

Solution 1: Grouping and Summing

We can use the if function or the least and greatest functions to convert from_id and to_id into person1 and person2, and then group by person1 and person2 and sum the values.

• # Write your MySQL query statement below
WITH caller as (
select from_id as person1, to_id as person2, duration
from Calls
UNION ALL
select to_id as person1, from_id as person2, duration
from Calls
),

unique_caller as (
select person1, person2, duration
from caller
where person1 < person2
)

select
person1, person2, count(*) as call_count, sum(duration) as total_duration
from unique_caller
group by person1, person2

--

SELECT
IF(from_id < to_id, from_id, to_id) AS person1,
IF(from_id < to_id, to_id, from_id) AS person2,
COUNT(1) AS call_count,
SUM(duration) AS total_duration
FROM Calls
GROUP BY 1, 2;