一、over(partition by ......)主要和聚合函数sum()、count()、avg()等结合使用,实现分组聚合的功能
示列:根据day_id日期和mac_id机器码进行聚合分组求每一天的该机器的销量和即sum_num,hive sql语句:select day_id,mac_id,mac_color,day_num,sum(day_num)over(partition by day_id,mac_id order by day_id) sum_num from test_temp_mac_id;
则hive sql语句为:select day_id,mac_id,sum(day_num) sum_num from test_temp_mac_id group by day_id,mac_id order by day_id;结果如下表
注:我们可以观察到group by可以实现同样的分组聚合功能,但sql语句不能写与分组聚合无关的字段,否则会报错,即group by 与over(partition by ......)主要区别为,带上group by的hive sql语句只能显示与分组聚合相关的字段,而带上over(partition by ......)的hive sql语句能显示所有字段.。