Query slows down after using Table.First Power Query

[MS1986]

Hi All,

I'm new to the Forum so sorry if this is posted in a wrong place.

I tried to find a solution on Google, but unfortunately, it seems that no one has stumbled upon a similar issue. 

I started using Power Query only recently, so I'm still learning. Anyway, I am trying to build an automated reporting for vendor expense map for my company. I have 4 data source files which are transformed and merged into one query with mappings applied. 

Problem starts when I try to Merge my Left Table with a mapping table which contains duplicates. In order to avoid duplicated lines (which is not expected for a final result) I use Table.First function and then the issue starts. Up until the function, everything works smoothly. When I apply the function a whole query slows down and takes ages to calculate. Any ideas on how to fix this would be much appreciated.

[ImkeF]

Remove the duplicates from your (right) lookup-table before merging it: Faster merge and no need to select first values afterwards.

(Create an intermediate table if you need the lookup-table in its original state in the data model)

[MS1986 · Accepted solution]

Thank you very much! I did exactly this last night trying to figure out the way. This helped and now the query works way smoother, I also included Table.Buffer for all  source tables and switched off the backroundupdates for queries. Now extracting 180k records takes approx 3-5mins. 

[ImkeF]

Good to hear!