Running Sum Window — Solution & ExplanationProblems / Running Sum Window / EditorialApproachA running (cumulative) sum adds each row's value to the total of all preceding rows in the partition.

Window frame: ROWS BETWEEN UNBOUNDED PRECEDING AND CURRENT ROW ensures every row from the partition start up to the current row is included.

Partition: By region so each region accumulates independently.

Order: By date so the sum accumulates chronologically.

Note: With an ORDER BY clause, many SQL engines default to RANGE BETWEEN UNBOUNDED PRECEDING AND CURRENT ROW, which produces the same result here since dates are unique within each region.Hints

A running total is SUM() with a window frame from UNBOUNDED PRECEDING to CURRENT ROW.

PARTITION BY region ensures each region's total is independent.

In PySpark, use Window.unboundedPreceding and Window.currentRow with rowsBetween().

Solve Running Sum Window yourself →