What is the main difference between ROLLUP and CUBE operations?

The correct choice highlights a fundamental difference in the behavior of ROLLUP and CUBE operations within the context of SQL and data aggregation.

ROLLUP is designed to aggregate data in a hierarchical manner, where it produces subtotals and grand totals for a set of specified dimensions. It creates a summary for each dimension step-by-step, thus reducing the dimensionality of the data progressively. For example, if you have data categorized by region and then by product, ROLLUP would first provide totals for each product, then more broadly for each region, and finally a grand total across all data.

CUBE, on the other hand, generates a comprehensive set of subtotals that includes all possible combinations of the specified dimensions. It creates a multidimensional view that includes all permutations of the grouping columns, allowing for a complete analysis of the data across all facets. This means that when using CUBE, every possible aggregation is considered, leading to a more exhaustive summary compared to ROLLUP.

Thus, the main difference lies in how they handle dimensions: ROLLUP reduces dimensions by providing subtotals in a hierarchical manner, while CUBE creates all possible combinations of the dimensions, providing a richer dataset for analysis.