Checking Columns Are Present In Power Query

Something I was meaning to mention in my previous post (but forgot about…) was that in a lot of cases you don’t really care if your output contains all the required columns – it’s enough just to check that your input contains all the required columns. Luckily M has a function called Table.HasColumns() to help you do this. For example, using the csv source file from my previous post, which should have three columns called Product, Month and Sales, the following query will return true if the source file has these columns and false if it doesn’t:

let
    Source = Csv.Document(File.Contents("C:\MissingColumnDemo.csv"),[Delimiter=",",Encoding=1252]),
    PromotedHeaders = Table.PromoteHeaders(Source),
    CheckColumns = Table.HasColumns(PromotedHeaders, {"Product", "Month", "Sales"})
in
    CheckColumns