Comparing Tables In Power Query

Power Query 1 Minute

An interesting Power Query nugget for you: you can compare two tables using the Value.Equals() function. For example, take the following worksheet with five Excel tables on it:

image

The following Power Query query compares Table 1 with each of the other four tables and tells me whether they are identical or not:

let

    Table1 = Excel.CurrentWorkbook(){[Name="Table1"]}[Content],

    Table2 = Excel.CurrentWorkbook(){[Name="Table2"]}[Content],

    Table3 = Excel.CurrentWorkbook(){[Name="Table3"]}[Content],

    Table4 = Excel.CurrentWorkbook(){[Name="Table4"]}[Content],

    Table5 = Excel.CurrentWorkbook(){[Name="Table5"]}[Content],

    Output = Table.FromRows(

                {

                {"Table2", Value.Equals(Table1, Table2)},

                {"Table3", Value.Equals(Table1, Table3)},

                {"Table4", Value.Equals(Table1, Table4)},

                {"Table5", Value.Equals(Table1, Table5)}

                },

                {"Compared Table", "Is Equal To Table 1"}

        )

in

    Output

 

All the code here is doing is loading the five Excel tables and then outputting a single table that shows the result of Value.Equals() when you compare the first table with the other four. Here’s the output:

I’ve tested this on tables sourced from SQL Server and quickly ran into a bug that crashed Power Query, but it seems as though Value.Equals() returns True when you pass it two identical tables and False when you pass it a table and a view which is just a SELECT * from that table. I wonder if there’s some extra metadata that allows Power Query to tell the difference between a table and a view? More research needed I think.

Overall this seems quite a handy trick to know about. This post has barely scratched the surface of what you can do with Value.Equals() though – you can compare any two values, not just tables, and you can specify your own function to do the comparison. As with so much of Power Query there’s a lot to learn… but that’s what makes it so fun!

You can download the sample workbook here.

Published by Chris Webb

My name is Chris Webb, and I work on the Fabric CAT team at Microsoft. I blog about Power BI, Power Query, SQL Server Analysis Services, Azure Analysis Services and Excel.

Published

8 thoughts on “Comparing Tables In Power Query”

    1. Hi Chris,

      in the example you build a table with the results “from scratch”. Is there the possibility to have a comparison with “joined” data in a merged query? Will say to have the comparison in a column at the end of a merged query to determine differences between columns. I didn’t manage to write a kind of if…then…else up to now…

      Best regs
      Patrick

      Reply
      1. Chris Webb – My name is Chris Webb, and I work on the Fabric CAT team at Microsoft. I blog about Power BI, Power Query, SQL Server Analysis Services, Azure Analysis Services and Excel.
        Chris Webb says:

        You know, I have an idea how to do this but it needs testing. If my idea works I’ll write a blog post explaining it!

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  6. Many thanks Chris!

    Thanks to your post, I’m now using this technique when I optimize my M-code. As I rewrite, I compare the results from the already-validated original query output with that of the revised version:

    let
    Table1 = OriginalQueryName,
    Table2 =RevisedQueryName
    Output = Value.Equals(Table1, Table2)
    in
    Output

    This ensures that I didn’t revise in such a way that the new output has some difficult-to-detect differences from the original.

    Reply