Difference between AS-WAS and AS-IS reporting in a Data Warehouse

Every DWH/ETL developer should be well versed about this concept, I was a couple of days back explaining the same to a person new in our team. That's when it struck me, why not a post on the same, so here goes. I will try to explain the same, giving an example.

Imagine a customer making monthly payments to a bank loan each month from January 2020 till May 2020, where at the end of the month of March, he changed his Address, he moved to a new county/district. This information will be captured in Customer dimension in EDW as below,

So you have your first customer record, which expires on 31st March, and a new record,which is currently active from 1st April 2020 till high end date.

Now imagine we have a transaction table as below with the 5 payment transactions as discussed before from January 2020 till May 2020, so customer has made 3 payments at his first address and the rest 2 at his new address.

Let us discuss now the AS-IS and AS-WAS concepts with this dataset, most EDW/Reporting systems use "AS-WAS" concept for grouping, as per this, suppose you are grouping the payment amount based on DISTRICT column in "AS-WAS", the result set would look as below,

So as you can infer from the result set above, in AS-WAS grouping, the snapshot as of Transaction date gets reported, i.e when T1, T2 and T3 payments were made, the customer was at Trivandrum, and later when T4 and T5 payments were made, he moved to Cochin.

However in "AS-IS" reporting, all payments are reported against the current active record of the customer, hence the full amount will be reported against Cochin in this case, see result set below to understand,

In AS-IS reporting, the measures reported against dimension attributes as of current date.