Redshift - 聚合函数调用可能没有嵌套的聚合或窗口函数

根据你的问题，你可以试试这个查询。

使用 SUM 和 CASE WHEN Expression。

select cust_name, 
       sum(case when day_count > 7 then sales_count else 0 end) as count_14,
       sum(case when day_count < 7  then sales_count else 0 end) as count_7
from sales
group by cust_name;
因为Aggregate functions ，不能多次嵌套。
如果你想修复 
sum(case when day_count > 7 then count(sales_count) else 0 end) 
你可以尝试写一个子查询来解决这个问题。
SELECT cust_name,
       sum(case when day_count > 7 then cnt else 0 end) as count_14,
       sum(case when day_count < 7 then cnt else 0 end) as count_7
FROM (
    SELECT cust_name,(case when day_count > 7 then 1
                           when day_count < 7 then 2
                           else null
                      end) grp,
          count(sales_count) cnt
    FROM sales
    GROUP BY cust_name,
             (case when day_count > 7 then 1
                   when day_count < 7 then 2
                   else null
             end)
WHERE grp is not null
GROUP BY cust_name