Done HW6

[sagar1023]

No description provided.

[super30admin]

1. Correctness:

   • Problem 1 (Game Play Analysis II): The solution correctly identifies the first login device for each player using ROW_NUMBER() and filtering for rank 1. This is a standard approach.
   • Problem 2 (Game Play Analysis III): The solution correctly calculates the running sum of games played using window functions. This is appropriate.
   • Problem 3 (Shortest Distance in a Plane): The solution correctly calculates the minimum distance between distinct points, though the join condition could be clearer (perhaps using p1.x < p2.x OR (p1.x = p2.x AND p1.y < p2.y) to avoid duplicate comparisons).
   • Problem 4 (Combine Two Tables): The solution correctly performs a left join to include all persons regardless of address. This is standard.
   • Problem 5 (Customers with Strictly Increasing Purchases): The logic appears correct but is somewhat complex. The HAVING clause condition could be more clearly documented.

2. Time Complexity:

   • Problems 1-4: These solutions have reasonable time complexity for their respective problems, typically O(n log n) for sorting/window functions or O(n^2) for the distance calculation.
   • Problem 5: The self-join could lead to O(n^2) complexity in the worst case, which might be improved with alternative approaches.

3. Space Complexity:

   • All solutions have reasonable space complexity, typically O(n) for storing intermediate results in CTEs or window function calculations.

4. Code Quality:

   • The code is generally well-structured and readable.
   • Suggestions for improvement:
     • Use more descriptive CTE names (e.g., "FirstLogins" instead of "CTE").
     • Add comments explaining complex logic, especially in Problem 5.
     • Consider formatting the SQL more consistently (e.g., consistent capitalization of keywords).
     • In Problem 3, the join condition could be more explicit about avoiding duplicate point comparisons.

5. Efficiency:

   • Problem 3 could be optimized by ensuring each point pair is only compared once.
   • Problem 5 might benefit from alternative approaches using LAG() or similar window functions to avoid the self-join.

Overall, the solutions are correct and demonstrate good SQL knowledge, but could benefit from improved readability and documentation.