SUM(...) OVER (PARTITION BY ... ORDER BY ...
RANGE UNBOUNDED PRECEDING)
The query below shows the difference between running total
(rt_sum) and (rt_csum) by the use of
RANGE UNBOUNDED PRECEDING. When the value of two
consecutive partitioned values is the same (9500 in query
below), then both will have the same total value (RT_CSum)
as shown in row 4 and 5 (Central/West region) for the year
2011 in the query below.