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Aggregation based on Date

Posted by sqlwiseguy on July 30, 2008

Imagine you have Sales database, we’ll use AdventureWorks, and you need to return the number of sales by product in the last 30, 90, and 180 days. How would you do this? In the past I might have used temp tables, table variables, or a union in order to get the the numbers for each date range. This would not be, in my opinion, the optimal way to retrieve this data. You could just return all the data with order dates and use Excel, SSRS, or another reporting tool to pivot the data, but once again this is probably not the optimal way to return the data. So, what do I think is the best way to do this? I do this in a single select filtering on the largest date range using CASE to return the data for the smaller date ranges. Here is the code, based on AdventureWorks (I use 7/1/2004 because that is the most recent order date in my copy of AdventureWorks):

SELECT
D.ProductId,
COUNT(H.SalesOrderID) AS sales_for_180,
SUM(D.ORderQty) AS no_products_sold_180,
SUM(CASE
WHEN H.OrderDate >= DATEADD(DAY, -90, '7/31/2004' ) THEN 1
ELSE 0
END) AS sales_for_90,
SUM(CASE
WHEN H.OrderDate >= DATEADD(DAY, -90, '7/31/2004' ) THEN D.OrderQty
ELSE 0
END) AS no_products_sold_for_90,
SUM(CASE
WHEN H.OrderDate >= DATEADD(DAY, -30, '7/31/2004' ) THEN 1
ELSE 0
END) AS sales_for_30,
SUM(CASE
WHEN H.OrderDate >= DATEADD(DAY, -30, '7/31/2004' ) THEN D.OrderQty
ELSE 0
END) AS no_products_sold_for_30
FROM
Sales.SalesOrderHeader H JOIN
Sales.SalesOrderDetail D ON
H.SalesOrderID = D.SalesOrderID
WHERE
H.OrderDate < '7/31/2004' AND
H.OrderDate >= DATEADD(DAY, -180, '7/31/2004')
GROUP BY
D.ProductId

This will return the data you asked for in a single pass and will do an index seek if you have an index on OrderDate. All in all an efficient way to return the desired data. You may have learned this a long time ago, but it is something I recently picked up when answering a question on SQLServerCentral, so I know not everyone knows this. This technique works whenever you need aggregates based on some sort of partition. It could be a breakdown of products within a product category as well.

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