Parallel Date Sales SQL View - sql

Question

I have a challenge which I can't seem to resolve on my own and now need help!
I have a requirement to show parallel year date sales via SQL and by that I mean if today (20/08/2015) Customer A has purchased products worth 500, I want to know how much Customer A spent on the same day last year (so 20/08/2014).
Here's a SQL fiddle where I've built everything (I reckoned that would be easiest for you guys). I have 3 dimensions (DimProduct, DimDate and DimCustomer), a fact table (FactSales) and a view (VW_ParallelSales) which I've built on top. I have also left a query on the right hand side with what I'm trying to achieve. If you run the query you will see that for Antonio, the SaleAmount on 20140820 was 3500 and if you look at the very bottom of the table, you can see there's one more record for Antonio in the fact table on 20150820 for 6500. So esentially, what I want is to have that 3500 which was sold on 20140820 (which is the parallel year date of 20150820) under the column ParallelSales (which at the moment is showing as NULL).
It all works like a charm if I don't include the ProductKey in the view and have just the CustomerKey (see this fiddle). However, as soon as I add the Product Key, because there is no exact match of CustomerKey-ProductKey that has happened in the past, I'm getting NULLS for ParallelSales (or at least that's what I think the reason is).
What I want to be able to do is then use the view and join on both DimCustomer and DimProduct and run queries both ways, i.e.:
Query 1: How much did Customer A spend today vs today last year?
Query 2: How much of Product A did we sell today vs today last year?
At the moment, as is, I need to have 2 views for that - one that joins the two sub-queries in the view on CustomerKey and the other one - on ProductKey (and obviously the dates).
I know it's a lot to ask but I do need to get this to work and would appreciate your help immensely! Thanks :)

Answer 1

For customer sales in diferent years.
SQL Fiddle Demo
SELECT DimCustomer.CustomerName,
VW_Current.Saledate,
VW_Current.ParallelDate,
VW_Current.CurrentSales,
VW_Previous.CurrentSales as ParallelSale
FROM DimCustomer
INNER JOIN VW_ParallelSales VW_Current
ON DimCustomer.CustomerKey = VW_Current.CustomerKey
LEFT JOIN VW_ParallelSales VW_Previous
ON VW_Current.ParallelDate = VW_Previous.Saledate
AND DimCustomer.CustomerKey = VW_Previous.CustomerKey
ORDER BY 1, 2
For productkey
SQL Fiddle Demo
With sales as (
SELECT
DimProduct.ProductKey,
DimProduct.ProductName,
VW_ParallelSales.Saledate,
VW_ParallelSales.ParallelDate,
VW_ParallelSales.CurrentSales,
VW_ParallelSales.ParallelSales
FROM DimProduct INNER JOIN VW_ParallelSales ON DimProduct.ProductKey =
VW_ParallelSales.ProductKey
)
SELECT
s_recent.ProductName,
s_recent.Saledate ThisYear,
s_old.Saledate PreviousYear,
s_recent.CurrentSales CurrentSales,
s_old.CurrentSales ParallelSales
FROM
SALES s_recent
left outer join SALES s_old
on s_recent.saledate = s_old.saledate + 10000
and s_recent.ProductKey = s_old.ProductKey