No need for data but if you can share the query, renaming the columns if you want, then it would at least give us a glimpse and help you write...

Without knowing the data or what you're trying to accomplish, we can't really help you.  Like 1 person mentioned, using UDF is not recommended as part of the query but...

The reason your query returned more results and the fact that it does, due to the DISTINCT clause, should be a red flag that there's something different about the data...