Completed SQL5

[alokusw2]

No description provided.

[super30admin]

1. Correctness:

   • Problem 1 (Report Contiguous Dates): The solution correctly identifies contiguous date ranges and labels them appropriately. The use of ROW_NUMBER() to create groups is a standard approach for this type of problem.
   • Problem 2 (Student Report By Geography): The pivot solution using CASE statements and ROW_NUMBER() is correct and handles the sorting requirement.
   • Problem 3 (Average Salary Department vs Company): The solution correctly compares department averages to company averages, though it could be more efficient.
   • Problem 4 (Game Play Analysis I): The simple GROUP BY solution is correct for finding first login dates.

2. Time Complexity:

   • Problem 1: O(n log n) due to sorting in ROW_NUMBER()
   • Problem 2: O(n log n) due to sorting in ROW_NUMBER()
   • Problem 3: O(n) for the window functions
   • Problem 4: O(n) for the GROUP BY operation

3. Space Complexity:

   • All solutions use O(n) space for intermediate results.

4. Code Quality:

   • The code is generally well-structured and readable.
   • CTEs are used appropriately to break down complex queries.
   • Variable names could be more descriptive (e.g., 'A', 'B', 'C' are not very meaningful).
   • Consistent formatting makes the code easy to read.

5. Efficiency:

   • Problem 3 could be optimized by calculating the company average once instead of repeating it for each row.
   • Problem 1 and 2 are already quite efficient for their problem types.
   • No major inefficiencies found.

Areas for Improvement:

• Use more descriptive CTE names
• For Problem 3, consider calculating the company average in a separate CTE
• Consider adding comments for complex logic