SQL6: Problem Solutions RN32MAY2025DS

[Feminto]

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[super30admin]

The student's solution demonstrates a good understanding of SQL queries and window functions. Here's a detailed evaluation:

1. Correctness:

• combine_two_tables: Correctly uses LEFT JOIN to include all persons even if they don't have an address.
• game_analysis_2: All three methods correctly find the first login device for each player. Method 3's use of DENSE_RANK() is particularly elegant.
• game_play_analysis_3: Both methods correctly calculate the running total of games played.

2. Time Complexity:

• All queries appear to have optimal time complexity for their respective problems, typically O(n) or O(n log n) for the sorting/grouping operations.

3. Space Complexity:

• The CTE in game_analysis_2 Method 1 creates temporary storage, but this is reasonable for the problem.
• The window functions in other methods are memory efficient.

4. Code Quality:

• Excellent use of formatting and indentation.
• Clear and descriptive column aliases.
• Multiple approaches shown where applicable, demonstrating good problem-solving skills.
• Minor typo in game_play_analysis_3 Method 2 ("FROm" instead of "FROM").

5. Efficiency:

• All solutions are efficient. The only potential improvement would be to add indexes on join/partition columns (personid, player_id, event_date) if these were production queries.

Areas for Improvement:

• The FIRST_VALUE window function in game_analysis_2 Method 2 has an unnecessary RANGE clause that could be simplified.
• Consider adding comments explaining why each approach might be preferred in different scenarios.