如何使用 sql-window 函数在 SQL 中创建计算列？

Question

So I am working on this solution that involves fetching input of 3 columns say 'Year', 'Month' and 'Spend' and use them to create another column 'Year Total' using logic that imitates SQL-window functions. For example, I need the following table given first three columns are editable,

|------------|-------|--------|----------|
|   Year     |Month  |  Spend |Year Total|
|------------|-------|--------|----------|
|    2018    |   Jan |  10    |   55     |
|    2018    |   Feb |  20    |   55     |
|    2018    |   Oct |  25    |   55     |
|    2019    |   Jan |  15    |   120    |
|    2019    |   Aug |  60    |   120    |
|    2019    |   Nov |  45    |   120    |
|------------|-------|--------|----------|

But calculating this in the frontend and on the fly is making the solution very slow. Hence I am trying to move this calculation to the backend in the SQL table using calculated columns. Basically, data will be written to the backend(SQL), columns calculated and re-read to show in frontend.

I have looked around a bit, only to find that windows functions cannot be used in calculated columns in SQL. Also, note that stored procedures are not allowed in the solution.

Can anyone suggest how to do this, or even if this is possible at all?

Note that frontend is Powerapps/Power BI

Answer 1

'using logic that imitates SQL-window functions' why?

You just need a join to a sub query which groups by year.

select t.* , s.sumspend
from <table> t
join (select year, sum(spend) sumspend from <table> group by year) s
on s.year = t.year;

Answer 2

Use a view:

create view v_t as
    select t.* ,
           sum(spend) over (partition by year) as year_spend
    from t;

Window functions are not allowed in generated columns.

SQL Server allows window functions in updatable views, so you will be able to modify the other columns. You will need to reload the table whenever a change is made, to get the updated data.