Window Functions Interview Questions

21 real Window Functions questions asked in live technical interviews — each with a model answer. Updated weekly.

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What is the difference between ROW_NUMBER, DENSE_RANK, and RANK window functions?🟡 Medium · Conceptual · Asked 1×How can you use a window function with DENSE_RANK to find the second highest salary in each department?🟡 Medium · Conceptual · Asked 1×How do you use a window function with DENSE_RANK to rank salaries within each department and filter for rank 2?🟡 Medium · Conceptual · Asked 1×How can you use a window function to retrieve the second highest salary per department?🟡 Medium · Conceptual · Asked 1×Given a dataframe, how would you keep only the latest record for each customer?🟡 Medium · Coding · Asked 1×Given the following table of customer events, write a SQL query to find the most recent status for each customer.🟡 Medium · Coding · Asked 1×Can you tell me the difference between RANK() and DENSE_RANK()?🟢 Easy · Conceptual · Asked 1×What other window functions are you aware of?🟢 Easy · Conceptual · Asked 1×How would you retrieve the top two orders by amount for each store for a given month?🟡 Medium · Coding · Asked 1×How would you retrieve the top two orders by amount for each store for a given month using PySpark?🟡 Medium · Coding · Asked 1×You need each customer's three most recent orders. How would you write that query?🟡 Medium · Coding · Asked 1×How would you write a SQL query to group each user's logins into consecutive‑day runs (gaps and islands) and then find the longest run per user?🟡 Medium · Conceptual · Asked 1×How would you add a column that calculates the rolling average of revenue per transaction timestamp, given that you only have a transaction timestamp column and no order date?🟡 Medium · Coding · Asked 1×How would you compute a 7‑day rolling average of daily revenue when there can be multiple transactions per day, using transaction timestamps?🟡 Medium · Coding · Asked 1×How would you modify your query to compute a 30‑day rolling average of daily revenue when you only have a transaction timestamp column and no order date?🟡 Medium · Coding · Asked 1×Write an SQL query to compute a 7‑day rolling average of daily revenue using a window function.🟡 Medium · Coding · Asked 1×How does this query calculate the rolling 7‑day average revenue using a window function?🟡 Medium · Conceptual · Asked 1×What is a better approach to find employees working on projects greater than or equal to the average number of projects per employee?🟡 Medium · Conceptual · Asked 1×How would you write a SQL query to find the first and last purchase dates for each customer-product pair, ensuring that each pair has at least two completed orders?🟡 Medium · Coding · Asked 1×Describe how you would use a CTE and window functions to rank purchases by date and then filter for the first and last occurrences for each customer-product pair.🟡 Medium · Coding · Asked 1×How would you use a Spark window function with row_number() partitioned by customer and ordered by timestamp descending to get the latest order per customer?🟡 Medium · Coding · Asked 1×

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