Measure Next-Day Return after Each Player’s First Login

### Problem Return fraction: the fraction of all players who logged in on the calendar day immediately after their first recorded login. Round to two decimal places. The denominator counts players, not activity rows; zero games still constitutes a login. ### Tables Table: `Activity` ```text +--------------+---------+ | 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. ``` ### Constraints `Activity` contains at least one row, so at least one player is present. Every event_date is a finite calendar date. ### Example ```text Activity (player_id,device_id,event_date,games_played): (1,2,2021-01-01,0), (1,3,2021-01-02,1), (1,3,2021-01-05,2), (2,2,2021-02-01,2), (2,2,2021-02-03,2) Output (fraction): (0.50) ``` ### What a Strong Answer Covers - Use each player's first recorded login and the calendar day immediately after it. - Count each player once and round the fraction to two decimal places. ### Follow-up Questions - How would you measure a return on the seventh calendar day? - How would you compare return rates by the month of the first login?