Date: February 06, 2026
Category: SQL
Time Taken: 20 minutes
Difficulty: Medium

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Problem Statement

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 determine the number of players who logged in on the day immediately following their initial login, and divide it by the number of total players.

Link: Game Play Analysis IV

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Approach:

• The first solution that comes to mind is to calculate the first_login dates from the table using MIN(event_date). This allows us to check if a date is the day after the first_login.

• The formula is the total number of players who log in the day after their first login, divided by all distinct players.

• We can calculate the total number of players with a subquery. We will join this with our CTE on their player_id, and if the event_date is just after the first_login, we will use DATE_ADD to achieve this.

Solution Code:

WITH first_logins AS (
    SELECT player_id, MIN(event_date) AS first_login
    FROM Activity
    GROUP BY player_id
)

-- first_login players / Total distinct players
SELECT ROUND(COUNT(DISTINCT a.player_id) / (SELECT COUNT(DISTINCT player_id) FROM Activity), 2) AS fraction

FROM Activity AS a
JOIN first_logins AS f

ON a.player_id = f.player_id AND a.event_date = DATE_ADD(f.first_login, INTERVAL 1 DAY)

Pattern: Aggregation and CTE.

Mistakes I Made: I initially had some trouble figuring out the logic.

Series: 90 Days of Data Engineering Progress: 35/90 problems completed

Tags: #DEQuest #LeetCode #SQL #DataEngineering #BuildInPublic