Completed SQL1

[alokusw2]

No description provided.

[super30admin]

1. Correctness:

   • Problem 1 (Big Countries): The solution correctly identifies big countries based on the given criteria using a simple WHERE clause with OR conditions. This is correct and efficient.
   • Problem 2 (Nth Highest Salary): The solution uses DENSE_RANK() to handle ties and correctly returns NULL if there are less than N distinct salaries. This is a correct approach.
   • Problem 3 (Delete Duplicate Emails): The solution correctly deletes duplicate emails while keeping the one with the smallest id using a self-join. This is a standard and correct approach.

2. Time Complexity:

   • Problem 1: O(N) where N is the number of rows in the World table, as it requires a full table scan.
   • Problem 2: O(N log N) due to the sorting operation in DENSE_RANK().
   • Problem 3: O(N^2) in the worst case due to the self-join, but this is acceptable for typical database sizes.

3. Space Complexity:

   • Problem 1: O(1) as it only returns a subset of rows without additional storage.
   • Problem 2: O(N) for storing the ranked results in the CTE.
   • Problem 3: O(1) as it modifies the table in place.

4. Code Quality:

   • The code is well-structured and readable. The use of CTE in Problem 2 is a good practice for clarity.
   • The solutions follow SQL best practices, such as using DISTINCT in Problem 2 to ensure only distinct salaries are considered.

5. Efficiency:

   • All solutions are efficient for their respective problems. No major optimizations are needed, but for Problem 3, an alternative approach using a subquery with GROUP BY might be more readable to some developers, though it would have similar performance.