Redshift中的ROW_NUMBER（）从每个组中选择最大行？

Question

我需要根据COUNT(1)字段从每个组中选择一行。

在其他数据库中，我使用ROW_NUMBER（）函数，该函数在redshift中为unsupported yet。

Answer 1

答案是使用SUM(1) OVER(PARTITION BY group_field ORDER BY order field ROWS UNBOUNDED PRECEDING)这样的结构：

SELECT id,
       name,
       cnt
FROM
  (SELECT id,
          name,
          count(*) cnt,
          sum(1) over (partition BY id ORDER BY cnt DESC ROWS UNBOUNDED PRECEDING) AS row_number
   FROM table
   GROUP BY id,
            name)
WHERE row_number = 1
ORDER BY name