Which clause completes the code to return the last updated time of the most recent row for each customer?

Which clause completes the code to return the last updated time of the most recent row for each customer?

• A. WHERE X = 1
• B. HAVING X = 1
• C. WHERE ROW = 1
• D. FILTER X = 1

Answer: (A)

Filter after ranking the rows within each customer. By using a window function like ROW_NUMBER() OVER (PARTITION BY customer_id ORDER BY updated_at DESC) AS X, you label each customer’s rows with X = 1 for the most recent one. The outer query then keeps only those rows with X = 1, returning the last updated time for each customer. HAVING would apply to grouped aggregates, not to the per-row result after windowing; FILTER is for aggregates as well, not for filtering the windowed result set.

Filter after ranking the rows within each customer. By using a window function like ROW_NUMBER() OVER (PARTITION BY customer_id ORDER BY updated_at DESC) AS X, you label each customer’s rows with X = 1 for the most recent one. The outer query then keeps only those rows with X = 1, returning the last updated time for each customer. HAVING would apply to grouped aggregates, not to the per-row result after windowing; FILTER is for aggregates as well, not for filtering the windowed result set.