to stop workflow when there is a duplicate in collumn a

Hey all,

Im trying to figure out how to stop a workflow containing a table to stop when there is a duplicate in collumn a (yes, its the ID-collumn :wink: ). I saw already a lot of ways to stop the workflow when a table is empty yet that means that this table is different from the orginal table. The original table is not empty but might have some duplicates in the ID-collumn.

I did figure out the worflow in the screenshot but that just throws an message instead of stopping the workflow.