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Author: mrinal1704

Medium/Game Play Analysis 4.sql

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+-- Question 91
+-- 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 of this table.
+-- This table shows the activity of players of some game.
+-- Each row is a record of a player who logged in and played a number of games (possibly 0) 
+-- before logging out on some day using some device.
+ 
+
+-- Write an SQL query that reports 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 query result format is in the following example:
+
+-- 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            |
+-- +-----------+-----------+------------+--------------+
+
+-- Result table:
+-- +-----------+
+-- | fraction  |
+-- +-----------+
+-- | 0.33      |
+-- +-----------+
+-- 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
+
+-- Solution
+With t as 
+(select player_id,
+ min(event_date) over(partition by player_id) as min_event_date,
+ case when event_date- min(event_date) over(partition by player_id) = 1 then 1 
+ else 0 
+ end as s
+ from Activity)
+
+select round(sum(t.s)/count(distinct t.player_id),2) as fraction 
+from t