Hi Tam,
Thanks for clarifying the scenario.
There are still multiple ways of doing this based on how the records in the first two columns were generated. However, this method will work.
1. Make sure one of the columns COL1 or COL2 is defined as a Unique/primary key in the table.
2. If we assume the initial data is part of the data pool definition, then when you add the new column you should see something like this:
3. Add the appropriate data to the new column COL3, and publish the data to target.
4. When you attempt the publish you will see a warning/error message:
Click "Update All Tables" on this dialog and continue with the publish.
5. You should see the expected results in the target table:
Hope that helps.
Cheers,
Sameer