문제
Table: Activity
+--------------+---------+
| Column Name | Type |
+--------------+---------+
| player_id | int |
| device_id | int |
| event_date | date |
| games_played | int |
+--------------+---------+
(player_id, event_date) is the primary key (combination of columns with unique values) of this table.
This table shows the activity of players of some games.
Each row is a record of a player who logged in and played a number of games (possibly 0) before logging out on someday using some device.
Write a solution to report the fraction of players that logged in again on the day after the day they first logged in, rounded to 2 decimal places. In other words, you need to count the number of players that logged in for at least two consecutive days starting from their first login date, then divide that number by the total number of players.
The result format is in the following example.
https://leetcode.com/problems/game-play-analysis-iv/description/
예시
Input:
Activity table:
+-----------+-----------+------------+--------------+
| player_id | device_id | event_date | games_played |
+-----------+-----------+------------+--------------+
| 1 | 2 | 2016-03-01 | 5 |
| 1 | 2 | 2016-03-02 | 6 |
| 2 | 3 | 2017-06-25 | 1 |
| 3 | 1 | 2016-03-02 | 0 |
| 3 | 4 | 2018-07-03 | 5 |
+-----------+-----------+------------+--------------+
Output:
+-----------+
| fraction |
+-----------+
| 0.33 |
+-----------+
Explanation:
Only the player with id 1 logged back in after the first day he had logged in so the answer is 1/3 = 0.33
문제 풀이
SELECT
ROUND(COUNT(DISTINCT player_id)
/ (SELECT COUNT(DISTINCT player_id) FROM activity),2) AS fraction
FROM
activity
WHERE
-- player_id와 이전 날짜를 사용하여 2일 연속 로그인 기록을 찾습니다
(player_id, DATE_SUB(event_date, INTERVAL 1 DAY))
-- 각 player_id별 최초 로그인 날짜를 찾습니다
IN (SELECT
player_id, MIN(event_date)
FROM
activity
GROUP BY
player_id);SQL을 독학하시는 분들에게 도움이 되길 바라며,
혹 더 좋은 방법이 있거나 오류가 있다면 편하게 말씀 부탁드립니다.
