现在，我们可从当前分组（或一个新开始的分组）中获得聚集信息，并将分组信息和传递给 UDF 的参数结合起来。

Now we get the aggregation information for the current group (or start a new group) and combine that group information with the parameters that were passed in to the UDF.

youdao

这是将分组信息编码到二进制串中的缘故，分组参数类型为VARCHAR，比简单的INTEGER类型潜在地要求更多的存储空间。

This is due to the encoding of the group information in the binary string, and a grouping parameter of type VARCHAR requires potentially more space than a simple INTEGER value.

youdao

如果利用相同的分组关键字或者没有分组关键字，来聚合多个列，那么，所有的聚合都在单个数据传递中的相同操作中进行。

If more than one column is aggregated using the same grouping key or without a grouping key, then all the aggregations are computed within the same operation with a single pass over the data.

youdao