在子查询中使用 datediff 计算历史年龄

Question

I'm trying to generate a view on open orders of an online store. I have a table with all orders and their respective dates (created_date, closed_cate), all of them are closed today.

In a first step I want to calculate the average age of open orders for any given day:

select
c.DATE,
 (SELECT avg(datediff('days', ord.ORDER_DATE, c.DATE))
    FROM "Orders" ord
        WHERE c.DATE>=ord.ORDER_DATE AND c.DATE<=ord.Order_close_date
    )
FROM CALENDAR c
WHERE c.DATE<=CURRENT_DATE() 
ORDER BY c.DATE desc

When executing this I'll receive an error code: "SQL compilation error: Unsupported subquery type cannot be evaluated"

Is there any way to solve this? The result should be an average for each day. Any input is highly appreciated!

Answer 1

One method is a recursive CTE:

with cte as (
      select o.order_date as dte, o.order_close_date, 0 as days_aging
      from "Orders" o
      union all
      select o.order_date + interval '1 day', o.order_close_date, days_aging + 1
      from cte
      where dte < o.order_close_date
     )
select dte, avg(days_aging)
from cte
group by dte;