Postgres - 如何使用最后行数的 AVG 并将其与另一列相乘？

Question

我有下表：

date     | ratio | revenue  
---------|-------|-----------
03-30-18 | 1.2   | 918264
03-31-18 | 0.94  | 981247
04-01-18 | 1.1   | 957353
04-02-18 | 0.99  | 926274
04-03-18 | 1.05  |
04-04-18 | 0.97  | 
04-05-18 | 1.23  |

如您所见，2018 年 4 月 3 日及以后尚未发生，因此这些天没有收入输入。但我对未来的日子有一个比例。我想使用我确实过去 4 天的平均收入，并将其乘以比率来做出未来的收入预测。

结果，我希望得到下表：

date     | ratio | revenue  
---------|-------|-----------
03-30-18 | 1.2   | 918264
03-31-18 | 0.94  | 981247
04-01-18 | 1.1   | 957353
04-02-18 | 0.99  | 926274
04-03-18 | 1.05  | 993073.73
04-04-18 | 0.97  | 917410.97
04-05-18 | 1.23  | 1163314.94

Answer 1

我认为不需要窗口函数，所以我将其表述为：

select t.date, t.ratio, 
       coalesce(t.revenue, a.avg4 * ratio) as revenue
from t cross join
     (select avg(revenue) as avg4
      from (select t.*
            from t
            where t.revenue is not null
            order by date desc
            limit 4
           ) t
     ) a
order by date;

Answer 2

您应该在初始查询中计算平均值，并使用

revenue

中包含空值的行的值：

with the_avg as (
    select avg
    from (
        select 
            date, 
            revenue, 
            avg(revenue) over (order by date rows between 4 preceding and current row)
        from my_table
        ) s
    where revenue is null
    order by date
    limit 1
    )
select 
    date, 
    ratio, 
    case when revenue is not null then revenue
    else round(avg * ratio, 2) end as revenue
from my_table
cross join the_avg
order by date;

SqlFiddle。