Whether it is a personal need to understand your spending pattern from looking at the bank transactions, or seeking to improve the sales performance in your organization by looking at the sales activities, the real insights are only visible with additional aggregation and summarization of the transactional level data.
Traditional RDBMSs provide this capability through the expressive power of SQL aggregation. Window functions were added to the ANSI SQL standard to further extend the ability to express more complex questions with the SQL construct.