Hi @Johan Van Noten​ ,

It seems like there is an issue with the columns that are part of your "where" clause. These columns are part of the UDF itself. I would like to recommend to the check the following docs

1) https://docs.databricks.com/spark/latest/spark-sql/language-manual/sql-ref-syntax-ddl-create-functio...

2) https://docs.databricks.com/spark/latest/spark-sql/language-manual/sql-ref-functions-udf-scalar.html

3) https://docs.databricks.com/spark/latest/spark-sql/language-manual/sql-ref-functions-udf-aggregate.h...

Hopefully, these link could be helpful to solve this issue.

Thank you.