Game Play Analysis I

Game Play Analysis I

What is this problem about?

The Game Play Analysis I interview question is a SQL task where you are given an Activity table. This table logs player logins, containing player_id, device_id, event_date, and games_played. Your goal is to write a query that reports the first login date for each player.

Why is this asked in interviews?

Companies like Amazon and Apple use this Database coding problem as a foundational test of your SQL aggregation skills. It evaluates if you know how to use the GROUP BY clause in conjunction with an aggregate function like MIN(). It's a very common real-world requirement for user analytics (e.g., finding a user's sign-up date or first action).

Algorithmic pattern used

This problem follows a basic Grouping and Aggregation pattern.

1. Use GROUP BY player_id to aggregate the rows for each individual player.
2. Use the MIN(event_date) function to find the earliest date in each group.
3. Select the player_id and the calculated minimum date, aliasing the column as first_login.

Example explanation

Activity Table:

player_id	event_date
1	2016-03-01
1	2016-05-02
2	2017-06-25

1. Group by player_id:
   • Group 1: [2016-03-01, 2016-05-02]
   • Group 2: [2017-06-25]
2. Find MIN for each:
   • Group 1 MIN: 2016-03-01
   • Group 2 MIN: 2017-06-25

Common mistakes candidates make

• Forgetting to alias: Not renaming the MIN(event_date) column to first_login as required by the problem description.
• Selecting un-aggregated columns: Trying to select device_id as well without putting it in the GROUP BY clause, which will cause a SQL error in strict modes (like ONLY_FULL_GROUP_BY in MySQL).
• Using ORDER BY instead: Trying to sort the whole table and use LIMIT, which doesn't work when you need the first date for every player, not just one.

Interview preparation tip

Always double-check the required output column names. SQL judging systems are very strict about aliases. This simple MIN() + GROUP BY pattern is the stepping stone to harder Window Function problems.