SQL Interview Questions 2026

Who Gets SQL Interviews

SQL rounds are required for: data engineers, data scientists, analytics engineers, and business intelligence roles. Some product manager roles at data-heavy companies also include SQL screens. For SWE roles, SQL rarely appears unless the role is backend with heavy database work.

The difficulty progression: SQL screens for analyst roles test joins, GROUP BY, and HAVING. Data scientist SQL tests window functions and self-joins. Data engineer SQL tests query optimization, partitioning, and schema design. Know which level applies to your target role.

Window Functions: The Differentiator

Window functions separate senior candidates from junior ones in SQL interviews. The most important to know: ROW_NUMBER() (unique rank per partition), RANK() and DENSE_RANK() (tied rank handling), LAG() and LEAD() (access previous/next row values), and SUM/AVG/COUNT OVER (running totals and moving averages).

The most common interview pattern using window functions: "Find the second-highest salary in each department." Solution: use DENSE_RANK() OVER (PARTITION BY department ORDER BY salary DESC), then filter WHERE rank = 2. Know why DENSE_RANK() is preferred over RANK() here (handles ties correctly).

Running total pattern: SUM(amount) OVER (PARTITION BY user_id ORDER BY date ROWS BETWEEN UNBOUNDED PRECEDING AND CURRENT ROW). The ROWS clause is frequently tested and frequently confused.

Complex Join Patterns

Know these join types cold: INNER JOIN (only matching rows), LEFT JOIN (all left rows, null for non-matching right), SELF JOIN (join table to itself for comparative queries), and CROSS JOIN (cartesian product, used for generating all combinations).

High-frequency SQL interview questions using joins: find users who made a purchase but never made a return (NOT EXISTS or LEFT JOIN with NULL check), find consecutive days of activity (self-join on date-1), find employees who earn more than their manager (self-join on manager_id).

Top SQL Interview Questions