Access the Derived Field Editor from a Data Source Configuration
To access the Derived Field Editor from a data source configuration:
Edit the data source configuration in the UI. See Edit a Data Source Configuration.
In the data source configuration wizard, select the Fields tab.
Scroll to the Derived Fields table at the bottom of the Fields tab.
Select to add a derived field. To modify a derived field, select the Type or Expression of the derived field on the Fields tab.
The Derived Field Editor appears.