Skip to main content
Showing results for 
Search instead for 
Did you mean: 

Find everything you need to get certified on Fabric—skills challenges, live sessions, exam prep, role guidance, and more. Get started

Helper I
Helper I

Do merge operations like Append store data twice?

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)

Super User
Super User

Hi @oneraj4u 


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

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

Hi @oneraj4u 


The own documentation of Microsoft: 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:

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 🙂

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

Helpful resources

July 2024 Power BI Update

Power BI Monthly Update - July 2024

Check out the July 2024 Power BI update to learn about new features.


Fabric Community Update - June 2024

Get the latest Fabric updates from Build 2024, key Skills Challenge voucher deadlines, top blogs, forum posts, and product ideas.

Top Solution Authors
Top Kudoed Authors