Three questions total, easy to medium difficulty.
First, restate the problem and clarify the expected output, then outline your logical steps before writing the query. Use CTEs to break the problem into manageable parts, and apply window functions to compute rankings, running totals, or comparisons across rows.
Pro tip: Always consider performance: window functions can be expensive, so filter early and avoid unnecessary sorting. Also, test your query with edge cases like ties or nulls to ensure correctness.
Identify the input table, columns, and the required output. Clarify any ambiguities about ordering, partitioning, or time windows.
Break down the problem into steps: what data to filter, what aggregations or rankings are needed, and how to combine results. Decide which window functions to use and their partitions/orderings.
Use CTEs to modularize the query. Start with a base CTE to select and filter raw data, then add CTEs for intermediate calculations using window functions.
Check for correctness with sample data, handle edge cases (ties, nulls, duplicates), and consider performance implications (e.g., indexing, avoiding unnecessary sorts).
AI-generated suggestions, not part of the candidate's original notes. May be inaccurate — verify before relying on them.