Creating SQL with multiple grouping sets.
创建具有多个分组集的sql。
This ROLLUP ends up being equivalent to the following grouping sets.
最终的这个ROLLUP相当于以下分组集。
Enumerations provide an alternative method of not only defining but also grouping sets of integral constants.
枚举提供了一种替代的方法，不但定义了整数常量集，而且还把它们聚集成组。
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