关于hive开窗函数的问题
如果over() 则开窗的聚合函数统计的所有行
如果over(partition by xx order by xx) 时，开窗的聚合函数统计的是相同partition by 后的字段按照order by 后的字段排序后区内行首到当前行，及相当于默认over(partition by xx order by xx rows between UNBOUNDED PRECEDING and current row)
如果over() 则开窗的聚合函数统计的所有行
如果over(partition by xx order by xx) 时，开窗的聚合函数统计的是相同partition by 后的字段按照order by 后的字段排序后区内行首到当前行，及相当于默认over(partition by xx order by xx rows between UNBOUNDED PRECEDING and current row)
