Classic SQL trap people think is easy until they actually write it out.
Start by clarifying the table schema and whether duplicates or ties should be considered. Then present a solution using either a subquery with MAX and a WHERE clause or a window function like DENSE_RANK, explaining the trade-offs. Finally, discuss edge cases such as fewer than two distinct values and how to handle them.
Pro tip: Mention that using DENSE_RANK handles ties correctly, but if the interviewer expects a simple subquery, be ready to switch. Also, explicitly state your assumption about distinct values and ask if the table could have fewer than two orders.
Ask about the table structure (e.g., order_id, order_value) and whether 'second highest' means second highest distinct value or second row when sorted. Confirm if ties should be considered.
Decide between a subquery-based solution (using MAX and exclusion) or a window function (DENSE_RANK or LIMIT/OFFSET). Consider performance and readability.
For subquery: SELECT MAX(order_value) FROM orders WHERE order_value < (SELECT MAX(order_value) FROM orders). For window function: SELECT order_value FROM (SELECT order_value, DENSE_RANK() OVER (ORDER BY order_value DESC) as rnk FROM orders) t WHERE rnk = 2.
Discuss what happens if there is no second highest value (e.g., return NULL or empty result). Mention how to handle duplicates and whether to use DISTINCT.
Walk through a sample dataset to verify correctness. If needed, discuss indexing on order_value for performance.
AI-generated suggestions, not part of the candidate's original notes. May be inaccurate — verify before relying on them.