Hi Walter Pelowski ,
Thankyou for using Microsoft Q&A platform and thanks for posting your question here.
As I understand your query, you want to remove the column entirely if all the records are null in that column with the help of mapping dataflow. Please let me know if that is not the correct understanding of your requirement.
Unfortunately, there is no direct way of achieving this in dataflow. Using rule based mapping in select transformation would allow us to remove a column based on its name or type , but not based on its column values.
Upon checking, All the suggestions I got was regarding replacing Null value to 'Unknown', the closest approach I could find is using combination of ADF activities and dataflow here: Dropping columns in Azure Data Factory based on values in columns . Please check if it helps.
Other way is to use stored procedure activity in ADF: How to detect and remove a column that contains only null values?
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