Question

An analyst needs to compute a running total of purchase amounts for each customer, ordered by transaction date, so that each row shows the cumulative spend up to and including that transaction. The source Delta table 'transactions' has columns customer_id, txn_date, and amount. Which Spark SQL expression produces the correct cumulative sum?

Accepted Answer

SUM(amount) OVER (PARTITION BY customer_id ORDER BY txn_date ROWS BETWEEN UNBOUNDED PRECEDING AND CURRENT ROW)

Answer

SUM(amount) OVER (PARTITION BY customer_id)

Answer

SUM(amount) GROUP BY customer_id, txn_date

Answer

SUM(amount) OVER (ORDER BY txn_date ROWS BETWEEN CURRENT ROW AND UNBOUNDED FOLLOWING)