In DESelect Segment, it is possible to Append, Update, or Overwrite the data. We refer to this as Data Action, similar to how it is called when creating a SQL Query Activity in Automation Studio.
To change this setting, click on the gear icon on the Target Definition screen, and choose Set Data Action. From the modal, you can select the Data Action you want to apply to your data and hit Save.
|Overwrite||Overwrite the current data in the Target Data Extension.|
|Append||Add results as new data to the Target Data Extension.|
|Update||Update existing records and add new records to the Target Data Extension.|