Hi,
This is a very common and frustrating issue! It almost always means that the data in one of your spreadsheets has changed. The Join tool itself isn't broken, but the uniqueness of your data is.
When a Join creates duplicates, it's because a key in your "one" dataset (your main set of data) is now matching to multiple records in your "many" dataset (the spreadsheet bringing in relevant data).
Here’s how to diagnose and fix it.
The Most Likely Fix: Use Both Matching Columns
You mentioned there is a second column you could match on. This is the key! You should almost always use all available matching columns to create the most specific match possible. This is called a composite key.
Open the configuration window for your Join tool.
In both the "Left" and "Right" input sections, make sure you have a checkmark next to both the ID column and the second matching column.
Run the workflow again.
This tells Alteryx to only create a match when both columns are identical, which will likely resolve your duplication issue immediately.
If this post solves your problem, please help our community by marking it as an accepted solution. This will make it easier for others to find the answer!
