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8.2
GROUP BY Clause Extensions
tion of aggregations. These summaries are sometimes called super aggre-
gates, as they are in actuality aggregations of aggregations, or summaries
of summaries.
The ROLLUP Clause
. The ROLLUP clause is best suited to build
two-dimensional summaries over multiple hierarchical layers.
The CUBE Clause
. The CUBE clause is best suited to production of
multiple dimensional summaries from a two-dimensional structure of
dimension and fact entities.
The GROUPING SETS Clause
. The GROUPING SETS clause is
effectively a filter, allowing selection of only required groupings pro-
duced by the ROLLUP and CUBE clauses.