A data warehouse contains data that has been aggregated for data analysis. You aggregate measures (such as quantities and amounts) for different entities (such as employees, customers, and products). You also determine the time units (e.g., day, month, year) for the aggregations according to your analysis needs. To allow fast query response, you might keep multiple summary tables, each containing a different time unit for the aggregations—for example, a table for daily aggregations, another...