Completed Q2_Sql1 Homework

[arushi2106]

Added SQL1_Q1_Solution.sql for the Big Countries LeetCode problem.

[BharathVuppala96]

Good Work

[super30admin]

Let me evaluate each solution separately:

1. Q1_Solution.sql:

• Correctness: Appears correct for finding countries with large area or population.
• Time Complexity: O(n) where n is number of rows in World table (full table scan).
• Space Complexity: O(1) - no additional space needed.
• Code Quality: Well-structured and readable. Good use of parentheses for clarity.
• Efficiency: Could benefit from indexes on area and population columns if this is a frequent query.

2. Q1_Solution_UsingDECLARE_SET:

• Correctness: Function name suggests it's for a different problem (Nth highest salary).
• Time Complexity: O(n log n) for sorting.
• Space Complexity: O(n) for sorting.
• Code Quality: Syntax error - missing column after "order by desc". Function name doesn't match purpose.
• Efficiency: LIMIT with offset can be inefficient for large N.

3. Q3_Sql1_solution.sql:

• Correctness: Correct approach to delete duplicate emails keeping lowest ID.
• Time Complexity: O(n log n) for window function and O(n) for deletion.
• Space Complexity: O(n) for temporary ranked_emails CTE.
• Code Quality: Well-structured using CTE. Clear logic.
• Efficiency: Good approach, though some databases might optimize self-join better.

4. SQL1_Q2_Question.sql:

• Correctness: Correct for finding Nth highest salary with dense_rank().
• Time Complexity: O(n log n) for sorting in window function.
• Space Complexity: O(n) for CTE.
• Code Quality: Good use of CTE and dense_rank(). IFNULL seems unnecessary since NULL would return anyway.
• Efficiency: Dense_rank() handles ties appropriately.

5. sql1_q3_crossjoin:

• Correctness: Correct for deleting duplicate emails keeping lower ID.
• Time Complexity: O(n^2) for cross join.
• Space Complexity: O(1) - no additional storage.
• Code Quality: Compact but less readable than CTE version. Could use comments.
• Efficiency: Cross join may be less efficient than window function approach for large tables.

General Observations:

• Good variety of approaches shown.
• Some solutions have syntax errors or naming mismatches.
• Window functions are generally preferred over self-joins for readability.
• Consistent indentation and formatting would improve readability across solutions.