தமிழில் - First Login Device | Advanced SQL Interview Questions | Data Engineer Interview Question

Video 362: This is the 37th video of the SQL Interview Question series.

00:00 - Introduction to dataset and Question
02:30 - Approach 1: CTE (Common Table Expression) Approach
04:50 - Approach 2: Subquery Approach
06:00 - Approach 3: Correlated Subquery Approach
08:00 - Approach 4: Concatenated Values Approach
10:40 - Approach 5: Window Function Approach
14:00 - Conclusion

We are given Activity table which shows the activity of players of some games. player_id, event_date is the primary key for this table

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.

We are asked to report the device that is first logged in for each player

In this video, we tackle an intriguing SQL problem: how to identify the first device each player logged in with?

** Approach 1: CTE (Common Table Expression) Approach **
We start by using a CTE to calculate the earliest login date for each player. This approach is clean and makes the query easy to read, especially for complex datasets.

** Approach 2: Subquery Approach **
Here, we employ a subquery to achieve the same result. This method is efficient and straightforward, perfect for scenarios where you want to nest your logic within the main query.

** Approach 3: Correlated Subquery Approach **
This technique leverages a correlated subquery to dynamically match each row with the earliest login date. It's a powerful approach when dealing with row-by-row comparisons.

** Approach 4: Concatenated Values Approach **
Using a clever IN clause with concatenated values, this approach matches player IDs and their respective first login dates directly within the main query. It's a concise method for solving the problem.

** Approach 5: Window Function Approach **
Lastly, we explore the power of window functions, specifically ROW_NUMBER(), to efficiently partition and order the data, allowing us to pinpoint the first login device for each player with precision.
Each method offers unique insights into SQL query writing, from readability and maintenance to performance considerations.

For a comprehensive understanding of these SQL methodologies and their application, please refer to this explanatory video.

code: https://github.com/jeganpillai/adv_sq...

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