CUME function is used to find running total. Similar to Moving Sum and Moving AVG.

CUME funciton adds the current row value to previous total and makes it as new total.
Syntax

CUME( numeric_value [, filter_condition] )

Argument	Required/Optional	Description
numeric_value	Required Numeric datatype. Passes the values for which you want to calculate a running total. You can enter any valid transformation expression. You can create a nested expression to calculate a running total based on the results of the function as long as the result is a numeric value.
filter_condition	Optional Limits the rows in the search. The filter condition must be a numeric value or evaluate to TRUE, FALSE, or NULL. You can enter any valid transformation
expression.

When a row has null value, CUME retains previous total. If all the rows have NULL value, CUME returns NULL for all rows.
Example : Find history of page views provided monthly page views

Month	Page Views	Total
Aug	300	300
Sep	400	700
Oct	500	1200