Completed Sql1

[NehaDhaliwal]

No description provided.

[Nandha2Tech]

Great Work!

[Nandha2Tech]

Great Work!

[super30admin]

Let me evaluate each solution separately:

Problem 1.sql:

1. Correctness: The query correctly selects countries with area >= 3 million or population >= 25 million, which appears to match typical "big countries" problems.
2. Time Complexity: O(n) where n is the number of rows in the World table, as it requires a full table scan.
3. Space Complexity: O(1) as it only returns a subset of rows without additional storage.
4. Code Quality: Simple and straightforward, follows good SQL practices.
5. Efficiency: No obvious improvements needed for this simple query.

Problem 2.sql:

1. Correctness: The solution correctly uses DENSE_RANK() to handle ties and returns NULL when N is out of bounds. However, the IFNULL(salary, NULL) is redundant - just returning salary would suffice.
2. Time Complexity: O(n log n) due to the sorting operation for DENSE_RANK().
3. Space Complexity: O(n) for the CTE storage.
4. Code Quality: Well-structured but could be simplified by removing the unnecessary IFNULL.
5. Efficiency: Consider adding an index on salary if this function is called frequently.

Problem 3.sql:

1. Correctness: The solution correctly deletes duplicate emails keeping only the record with the smallest id.
2. Time Complexity: O(n^2) due to the cross join, which could be problematic for large tables.
3. Space Complexity: O(1) as it operates in-place.
4. Code Quality: Clear and concise, though a self-join might be more readable than a cross join with a where clause.
5. Efficiency: For large tables, consider using a temporary table or window functions (DELETE FROM Person WHERE id NOT IN (SELECT MIN(id) FROM Person GROUP BY email)) which would be more efficient.

General improvements:

1. Problem 2 could be simplified by removing redundant IFNULL.
2. Problem 3 could be optimized for large datasets.
3. Adding comments explaining the logic would improve maintainability.