Running total between two dates SQL - sql

Question

I have a problem with building an efficient query in order to get a running total of sales between two dates.
Now I have the query :
select SalesId,
sum(Sales) as number_of_sales,
Sales_DATE as SalesDate,
ADD_MONTHS(Sales_DATE , -12) as SalesDatePrevYear
from DWH.L_SALES
group by SalesId, Sales_DATE
With the result:
| SalesId| number_of_sales| SalesDate|SalesDatePrevYear|
|:---- |:------:| :-----:|-----:|
| 1000| 1| 20200101|20190101|
| 1001| 1| 20220101|20210101|
| 1002| 1| 20220201|20210201|
| 1003| 1| 20220301|20210301|
The preferred result is the following:
| SalesId| number_of_sales| running total of sales | SalesDate|SalesDatePrevYear|
|:---- |:------:| :-----:| :-----:|-----:|
| 1000| 1| 1 | 20200101|20190101|
| 1001| 1| 1 | 20220101|20210101|
| 1002| 1| 2| 20220201|20210201|
| 1003| 1| 3|20220301|20210301|
As you can see, I want the total of Sales between the two dates, but because I also need the lower level (SalesId), it always stays at 1.
How can i get this efficiently?

Answer 1

You have successfully gotten the result which gives you the start and end dates that you care about, so you just need to take this result and then join it to the original data with an inequality join, and then sum the results. I suggest looking into the style of using CTE's (Common Table Expressions) which is helpful for learning and debugging.
For example,
WITH CTE_BASE_RESULT AS
(
your query goes here
)
SELECT CTE_BASE_RESULT.SalesId, CTE_BASE_RESULT.SalesDate, SUM(Sales) AS Total_Sales_Prior_Year
FROM CTE_BASE_RESULT
INNER JOIN DWH.L_Sales
ON CTE_BASE_RESULT.SalesId = L_Sales.SalesId
AND CTE_BASE_RESULT.SalesDate >= L_Sales.SalesDATE
AND CTE_BASE_RESULT.SalesDatePrevYear > L_Sales.SalesDATE
GROUP BY CTE_BASE_RESULT.SalesId, CTE_BASE_RESULT.SalesDate
I also recommend a website like SQL Generator that can help write complex operations, for example this is called Timeseries Aggregate.
This syntax works for snowflake, I didnt see what system you're on.
Alternatively,
WITH BASIC_OFFSET_1YEAR AS (
SELECT
A.Sales_Id,
A.SalesDate,
SUM(B.Sales) as SUM_SALES_PAST1YEAR
FROM
L_Sales A
INNER JOIN L_Sales B ON A.Sales_Id = B.Sales_Id
WHERE
B.SalesDate >= DATEADD(YEAR, -1, A.SalesDate)
AND B.SalesDate <= A.SalesDate
GROUP BY
A.Sales_Id,
A.SalesDate
)
SELECT
src.*, BASIC_OFFSET_1YEAR.SUM_SALES_PAST1YEAR
FROM
L_Sales src
LEFT OUTER JOIN BASIC_OFFSET_1YEAR
ON BASIC_OFFSET_1YEAR.SalesDate = src.SalesDate
AND BASIC_OFFSET_1YEAR.Sales_Id = src.Sales_Id