Like the counting function, when several aggregations with grouping keys are used in a rule, the group and count operations must be cascaded as shown in figure 14.
与计数函数类似，当在一个规则中使用多个具有分组关键字的聚合，对分组与计数操作必须进行级联，如图14所示。
For this new function, additional fields in message descriptor were needed to keep information for the segmenting and grouping.
对于该新功能，需要在消息描述符中附加字段来保留分段和分组信息。
You can compute aggregations on the whole column, or on subgroups that are specified by the grouping column given as the second parameter of the function.
可在整个列上计算聚合，或者由作为函数的第二个参数所给出的分组列指定的子组上计算聚合。
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