CUBE和ROLLUP  ROLLUP是Oracle8i以来一个新的SQL关键字，9i ,-11G不新鲜了，它是对GROUP BY子句的扩充，允许在SELECT语句中计算不同层次的小计。

CUBE是对GROUP BY子句的另外一  种扩充，它允许计算所有小计可能的组合，用来生成各种汇总报表。

以下介绍他们的用法

select B,c,D from Atest group by rollup(B,C,D);

相当于

select B,c,D from Atest group by B,C,D;

union all

select B,c,null from Atest group by B,C

union all

select B,null,null from Atest group by B

select B,c from Atest group by cube(B,C);

将所有 (B,C)组合的子集group by合并

相当于

select B,c from Atest group by B,C

union all

select B,null from Atest group by B

union all

select null,c from Atest group by c

union all

select null,null from Atest group by null

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