Following on from my previous post, let’s now look at how you can add derived columns to a table expression. Let’s start with a simple query that returns every column in DimDate:

evaluate(
DimDate
)

If I want to add some columns to this query without doing any grouping we can use the AddColumns function like so:

evaluate(
AddColumns(
DimDate
, “Calendar Year Name”
, “Calendar Year ” DimDate[CalendarYear]
)
)

Here I’m adding a new column (shown on the far right in the resultset in the above screenshot) called Calendar Year Name that does a simple concatenation of the string “Calendar Year” with the actual Calendar Year value from the table. You can add multiple columns in this way with more than one column name/expression pair.

The important thing to notice here is that you can’t use this new column to group by in a Summarize() function, so the following query:

evaluate(
Summarize(
AddColumns(
DimDate
, “Calendar Year Name”
, “Calendar Year ” DimDate[CalendarYear]
)
, [Calendar Year Name]
–, DimDate[CalendarYear]
, “Sum of Sales”
, Sum(FactInternetSales[SalesAmount])
)
)

…gives results you may not be expecting: instead of getting the sum for each year, you get the sum for all years repeated; I’m told this scenario may be changed to throw an error at RTM. AddColumns() should only be used for formatting a resultset.

If you uncomment the line grouping by DimDate[CalendarYear], you’ll see you get meaningful results:

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