如何采取上个月的结果sql [英] how to take previous month result in sql

问题描述

我有两个表'ms'和'fr'。

'ms'包含pid，month和totalsales，同时'fr'包含pid，month，n预测。在两个表中，每个pid有12个基于月的记录。

我实际上想要计算公式=（0.3 * totalsales）+（0.7 *上个月的预测结果）的需求。上个月的预测结果就像用户选择pid2和第2个月一样，然后将第1个月的预测结果作为计算数据。



我已经尝试了但是想要的结果还没有出来。

以下是我的代码

i have 2 tables which is 'ms' and 'fr'.
'ms' contain the pid,month, and totalsales meanwhile 'fr' contain pid, month, n forecast. IN both table, each pid has 12 record based on month.
i actually want to calculate the demand where the formula is = (0.3* totalsales)+(0.7* previous month result of forecast). The previous month result of forecast is like when the user choose pid2 and month 2 , then it will take the forecast result from month 1 as its calculation data.

i tried it already but the desired result is not coming out.
below is my code

select ((0.3*totalsalesamount)+(0.7*forecastdemand)) as demand from Monthlysales, forecastreorder where Monthlysales.P_ID = forecastreorder.Productid and Monthlysales.P_ID = 1 and forecastreorder.Month = 2

当我执行上面的代码时，结果基于他们的每个预测结果。例如，当我选择pid 1，第2个月时，它也将从第2个月获取预测结果。同时我希望它将第1个月的预测结果作为计算数据。

我该怎么做？

请帮帮我，谢谢高级：）

when i execute the code above, the result is based on their each forecast result. for example, when i choose pid 1, month 2, then it will take the forecast result from month 2 also. meanwhile i want it to take the forecast result from month 1 as its calculation data.
how can i do that??
please help me, thanks in advanced :)

推荐答案

试试这：

Try this:

select ((0.3*totalsalesamount)+(0.7*forecastdemand)) as demand
from Monthlysales join forecastreorder
on Monthlysales.P_ID = forecastreorder.Productid
where Monthlysales.P_ID = 1
and Monthlysales.month = 2
and forecastreorder.Month = 1

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