SQL5 problem solutions

[Feminto]

No description provided.

[super30admin]

The student has provided three different methods to solve the problem of finding the first login date for each player, which demonstrates good problem-solving skills and knowledge of different SQL approaches.

Strengths:

1. Method 1 is the simplest and most efficient solution, using GROUP BY with MIN() which is optimal for this type of problem.
2. Method 2 shows knowledge of window functions (FIRST_VALUE) though it's unnecessarily complex for this specific problem.
3. Method 3 demonstrates understanding of DENSE_RANK() and subqueries, though again more complex than needed.
4. All methods are syntactically correct and would return the expected results.

Areas for improvement:

1. Method 2 has an incorrect window frame specification (RANGE BETWEEN UNBOUNDED PRECEDING AND UNBOUNDED FOLLOWING) which is unnecessary for FIRST_VALUE. The default window frame would suffice.
2. Method 3 uses DENSE_RANK() when ROW_NUMBER() would be more appropriate since we only want the first row per player.
3. The solution could benefit from comments explaining why each method works and when one might be preferred over others.
4. There's no indication of handling NULL values or empty tables, though this might not be required by the problem.

Time Complexity:

• Method 1: O(n) for the scan plus O(m log m) for grouping (where m is number of players)
• Method 2: O(n log n) for the window function partition and sort
• Method 3: Similar to Method 2, O(n log n)

Space Complexity:

• Method 1: O(m) for the groups
• Methods 2 and 3: O(n) for the window function computations