Comparing columns error

[Necrosis1968]

Hi, sorry first time here and a PowerBI newbie.

I want to compare 2 columns, from different tables in PowerBI. They are joined by Unique-ID. I have tried the following:

Resolved = IF ('report last month'[Unique ID]= 'report this month'[Unique ID], "No", "Yes")

So basically, if it's in last month's report but not in this one then resolved=No for that row, else it will be Yes. If it's not disappeared from the report it's not resolved.

Problem is I'm getting an error "A single value for column 'Unique ID' in table 'report this month' cannot be determined." 

They are both String variable types.

I did try using MAX function but it sets every row in the resolved column as "Yes". I also tried MIN, but that sets all bar one as "Yes"

Any help appreciated. 

[v-rzhou-msft · Accepted solution]

Hi @Necrosis1968 ,

According to your statement, I think your error may be caused that you use 'report this month'[Unique ID] directly in your code to create the calculated column.

This error occurs because Power BI is unable to determine which row of data to use in a calculation among multiple rows of data.

Here I create a sample and I can reproduce your issue.

Last Month:

This Month:

Error:

I suggest you to try code as below.

Resolved = IF ('report last month'[Unique ID] in  VALUES('report this month'[Unique ID]), "No", "Yes")

Result is as below.

Best Regards,
Rico Zhou

If this post helps, then please consider Accept it as the solution to help the other members find it more quickly.

[Necrosis1968]

That worked! Thank you so much!

[HotChilli]

You have written a measure (which requires an aggregation). Are the 2 different tables related? This is what powerbi uses to work out the measure.