Start by generating the query using the first aggregation function ( SUM in the example) in the measure's list of aggregations to aggregate the template expression. 先使用度量的聚合列表中的第一个聚合函数(在这个示例中是SUM)对表达式模板进行聚合,产生一个查询。
An aggregate expression represents the application of an aggregate function across the rows selected by a query. 一个聚集表达式代表一个聚集函数对一个查询选出的行的处理。
Cannot perform an aggregate function on an expression containing an aggregate or a subquery. 中文说:不能对包含聚合或字查询的表达式执行聚合函数。
However, you do need an aggregate expression if you are using series groups. 但是,如果使用的是序列组,就需要聚合表达式。