Do merge operations like Append store data twice?

[oneraj4u]

I am trying to understand how Power BI stores data.

If I append Table A to Table B to create Table C:
Does Power Query / Power BI duplicate the data from A & B to create C and  store it twice thereby doubling the size of the file / data model?

( I am asking because I cannot disable the load of my tables, as I use SSMS to load data via XMLA endpoints. This is because the dataset is to large to publish, and it times out if I attempt to refresh it using native functionality in Power BI Service)

[mlsx4]

Hi @oneraj4u 

As far as I know, you're right. It stores data twice.

[oneraj4u]

Thanks for your response!  
Do you have a link to any documentation on the matter per chance?

[mlsx4]

Hi @oneraj4u 

The own documentation of Microsoft: https://learn.microsoft.com/en-us/power-query/append-queries Also, if you try to remove one of the appended tables it will give you an error. The only solution may be to apply SQL to join them before importing data into Power BI. There are lot of links on how to do it. For instance:

• https://community.fabric.microsoft.com/t5/Power-Query/Join-data-sources-before-importing-data/td-p/3...)
• https://www.youtube.com/watch?v=UQJAHUUFK-o

[oneraj4u]

I appreciate your effort, unfortunately I did not see anything about the storing of data in the Microsoft documentation.
I don't have any issues or questions regarding how to Append or the behaviors, just the storage.
Thanks for your time 🙂

[oneraj4u]

Just as a follow up - i use XMLA endpoints in SSMS, not SQL.