What is best practice to deal with missing data according to Kimball? - powerbi

Question

I have a data base with the following tables:
Customers, Invoices, Salesman, Target.
The ones concerned about my question are Customers, Invoices.
There are customersIDs used in the Invoices but doesn't exist in the Customers table.
If I used only the customers from Customers Table, my customer dimension would be incomplete.
My solution is to append these IDs from Invoices to Customers and fill other columns in the Customers table with nulls.
I don't know if this is the best approche according to Kimball?
also, if it is a good solution, how can I add accomplish it with Power bi desktop?
Customers table: "generated Data"
Invoice table:
..... just a sample the table is thousands of rows.

Answer 1

There's two points here:
Firstly, (in import mode at least) PBI already creates the "blank row" for items present in your fact table but missing from your dimension table for precisely this scenario. If you don't need the granularity of each individual missing customer id, then you don't need to do anything.
Secondly, if you need to to retain that granularity then your approach is the correct one. The way to do this in Power Query is as follows:
Create a new query which takes your customer dimension table and does a left outer join on customer id with your invoice fact table.
Expand the newly joined table but retain only the new customer id column.
Remove all columns apart from the new customer id column.
Remove duplicates
You now have a list of missing customer ids. Ensure the column name is the same as the column name of you customer id in the customer dimension table. Append this to the original customer dimension query and the nulls will be filled in automatically for the missing columns.

Answer 2

Please keep in mind that It is Kimball, not Kimble.
There are 4 steps of DWH Methodology:
1) Understand Business Process (What your process is actually measuring?)
2) Deciding the grain (It means what every row in your fact table actually represents?)
3) Deciding Dimensions (Ask Where-What-Who-Where-How-HowMany-HowMuch to your grain declaration formed together with business processing)
4) Define Facts (Metrics)
According to this order, You define Dimension tables before building your fact tables: If your dimension table , Customer table in this case, is missing in terms of customers available in your fact table, My biggest biggest advice according to the DWH Dimensional Modeling is to set your customer table right!!! Define every piece of customer in your dimension table!!!! Then populate your Fact table with records:
[Customer ID] in Customer Table : PRIMARY KEY
[CustomerID] in Invoice Table : FOREIGN KEY
SQL and Power BI reacts very differently in your problem:
1) Power BI has no referential integrity concept: It adds a blank row to your dimension table in such a case.
2) SQL gives referential integrity error, and you can't even add rows to your fact table. I support SQL in this case personally!!!!
Finally: Use some ETL tool(SSIS, Talend, ODI or even Power Query) to make your dimension table as accurate as possible:
For example:
Do not leave any column value as null!
If an unknown date exists, put a default date value like '1900-12-31'
If an unknown textual property, put in keywords 'unknown','not available' etc..
Because dimensional table are sources of querying in SQL statements; and different SQL Vendors (SQL Server, Oracle, MySQL) has to deal with NULL values in a different way, and this cause problems in terms of performance wise!!