可以用context by针对品种分组,然后用having,对每一个组内的数据用rowNo()函数进行过滤输出。
例子如下,对一组数据根据id的种类每组采样20个样本:
a = table(rand(`a`b`c,2000) as id, rand(50.0,2000) as price,1..2000 as rowno)
select * from a context by id having rowNo(id) in (0 join (rowNo(id).max()/18*1..18) join (rowNo(id).max()))