how to make a column relation in backendless database?
https://backendless.com/docs/rest/data_set_add_relation_rest.html - for REST API
https://backendless.com/docs/android/data_relations_set_add_overview_android.html - for Android SDK.
Also you can do it manually : Data Management -> Table you want to create relation from -> Schema -> New
and create new relation column, chose type
Data Object Relationship, chose table to relate, and type of relation.