Chris Webb wants to make your joins in Power Query faster:
The first question I decided to investigate was this:
Does the number of columns in a table affect the performance of a merge?
First of all, I created two identical queries called First and Second that connected to the CSV file, used the first row from the file as the headers, and set the data types to all seven columns to Whole Number.
Click through for the answer to this question. Chris promises a series out of this and I would expect there to be enough content for that.