#PowerQuery – Control the expand columns so it includes new columns

Image a scenario where your column in your PowerQuery that contains a table with a set a columns that you know at some point will have more columns added.

In the case above I know that we at some point will add more columns in the merged ProductAttributes table.

How can we make this dynamic using PowerQuery

When we click the icon for expanding the table, we might just select this and move on

But notice the formula created in

It says

= Table.ExpandTableColumn(#”Merged Queries”, “ProductAttributes”, {“Brand”}, {“Brand”})

This means that even though we might add new columns to the ProductsAttributes table – it will still only be Brand that is expanded and only that column.

The bolded arguments is 2 lists that contains the Column names to expand and the new names of the columns – the last argument is optional so we can actually skip that if we want the original names – https://docs.microsoft.com/en-us/powerquery-m/table-expandtablecolumn

Now by changing the formula to this

= Table.ExpandTableColumn(#”Merged Queries”, “ProductAttributes”,List.RemoveItems(Table.ColumnNames(#”Merged Queries”[ProductAttributes]{0}), {“ProductKey”})
)

We can make the table dynamically expand when adding new columns in the table ProductAttributes

We get the new column included as well

The magic formula does this

Table.ColumnNames(#”Merged Queries”[ProductAttributes]{0})

Will return a list of column names from the step before
expansion (note I use the step name and column name) – and I use the {0} to extract the column names only form the first row – otherwise the formula will fail.

But as we cannot have the same column names twice (i.e. ProductKey needs to go away) so we need to use the List.RemoveItems functions

List.RemoveItems(Table.ColumnNames(#”Merged Queries”[ProductAttributes]{0}), {“ProductKey”})

Thereby removing the ProductKey Item in the list

And this means that when we get more columns in the table “ProductAttributes” table they will automatically be included in the expanded columns

Hope this can help you power queries even more dynamic.

Here is an example file – Link

Power Query On !