如何在Teradata中按排名（而非行）计算滚动平均值？

Question

我具有 Teradata中的下表：

 ranked | data_val 
-------- ----------
 1      | 100
 2      |  30
 2      |  20
 2      |  70

我想要下表，其中avg_val是data_val值的滚动平均值，通过递增ranked值来排序：

 ranked | avg_val 
------ ---------
 1      | 100
 2      |  55

---

我尝试使用：

SELECT 
    ranked
  , AVERAGE(data)val) OVER (
      PARTITION BY NULL 
      ORDER BY ranked ASC
      ROWS UNBOUNDED PRECEDING
      ) AS avg_val
  FROM tbl
;

但是我明白了：

 ranked | avg_val 
------ ---------
 1      | 100
 2      |  65
 2      |  50
 2      |  55

这不是我想要的。

如何返回所需的输出？

Answer 1

如何使用窗口函数进行聚合？

select ranked,
       (sum(sum(data_val)) over (order by ranked rows between unbounded preceding and current row) /
        sum(count(*)) over (order by ranked rows between unbounded preceding and current row)
       )
from t
group by ranked;