Can I relate Data Extensions on multiple fields?

yes, in case you want to create a relationship between two data extensions on more than one field you have the ability to do so after dragging and dropping a data extension on top of another on the selection home page the create relationship modal shows up there, you have the ability to define as many additional relationships between two data extensions as you want by using the add relationship button more details on how this functionality works can be found below https //support deselect io/hc/en us/articles/360015480678