Efficiently create junk dimensions in power query

[robarivas]

I have a large fact table (many millions of rows). It has a bunch of columns in it that I'd like to break out into a few junk dimension tables. However, I have no keys to work with so I was planning on creating surrogate primary keys fo each junk dimension table. However, this means I then have to merge these tables back on to the fact table so that the fact table can obtain the proper foreign keys. I suspect this sort of multiple (self) joins/merges might bring the loading and refresh process to its knees. So is there a best practice way to acheive this whole procedure in an efficient (hopefully quick) way? I'd like to do it all in power query if possible. The fact table lives in a remote SQL Server.

[ImkeF]

Hi @robarivas 

Multiple levels of merge tend to become slow in PQ. Why not generate some views on the SQL Server already?

Or write them as SQL-queries in PQ.

[robarivas]

Thank you @ImkeF . Just to clarify: Are you saying I should create the junk dimensions on SQL server? That seems easy and logical. However, wouldn't I still need to merge those tables back to the fact table so that the fact table can obtain the keys. Or are you saying that this step should also be done on the SQL Server side?

[ImkeF · Accepted solution]

Hi @robarivas 

yes, doing everything on the server-side would probably be the fastest version.

It's not that PQ cannot do it, but SQL would be faster with it. Just create views for it that you then query.