Added five solutions/SQL6

[hinduja97]

No description provided.

[super30admin]

Let me evaluate each solution file separately:

problem1.sql:

• Correctness: This appears to correctly find the first login device for each player using RANK() which is a standard approach.
• Time Complexity: O(n log n) due to the window function sorting.
• Space Complexity: O(n) for storing the CTE.
• Code Quality: Well-structured and readable. Good use of CTE and window function.
• Efficiency: Could potentially use FIRST_VALUE() instead for better readability.

problem2.sql:

• Correctness: Correctly calculates the running total of games played per player.
• Time Complexity: O(n log n) for the window function.
• Space Complexity: O(n) for the result set.
• Code Quality: Simple and effective solution. Good use of window function.

problem3.sql:

• Correctness: Correctly finds the shortest distance between any two points.
• Time Complexity: O(n^2) due to the self-join.
• Space Complexity: O(n^2) for the join result.
• Code Quality: Could be improved by using a more descriptive alias than 'c' and 'p'.
• Efficiency: The self-join approach is correct but could be optimized for large datasets.

problem4.sql:

• Correctness: Correctly joins person and address tables with LEFT JOIN to include all persons.
• Time Complexity: O(n) for the join operation.
• Space Complexity: O(n) for the result set.
• Code Quality: Simple and effective. Good use of LEFT JOIN.

problem5.sql:

• Correctness: The logic to find customers with increasing spending year over year seems correct but complex.
• Time Complexity: O(n^2) due to the self-join.
• Space Complexity: O(n) for the CTEs.
• Code Quality: The logic is somewhat complex and could benefit from comments explaining the approach.
• Efficiency: The HAVING clause logic is clever but might be hard to maintain.

General feedback:

• The solutions demonstrate good understanding of SQL concepts like CTEs, window functions, and joins.
• Code is generally well-structured and readable.
• Some solutions could benefit from comments explaining complex logic.
• Variable/alias naming could be more descriptive in some cases.
• The solutions handle edge cases well (like NULL values in LEFT JOIN).