SQL Ranking Quant Interview Guide
SQL ranking quant interview guide for row_number, rank, dense_rank, partitioning, tie behavior, latest-row queries, and examples.
Candidates solving top-N, leaderboard, and latest-row queries.
Ranking functions order rows inside groups
ROW_NUMBER, RANK, and DENSE_RANK assign positions inside an ordered partition. They are common for top-N and latest-row tasks.
Tie behavior differs
ROW_NUMBER breaks ties arbitrarily unless additional ordering is specified. RANK leaves gaps after ties, while DENSE_RANK does not.
Concrete example
To get the latest trade per symbol, partition by symbol, order by timestamp descending, assign row_number, and filter to one.
Order needs determinism
If timestamps tie, add a deterministic secondary order such as id when available. Otherwise the selected row may not be stable.
Common mistakes
Candidates often forget partitioning and rank the entire table. State whether the top row is global or per group before filtering.
Practice the pattern
Use the LeetQuidity curriculum and calibration to turn this topic into a focused practice plan.