as far you are remember since many versions of Dynamics NAV (formerly Navision) you have to use a PRIMARY Key field when using the table relation
If not, you are running into the issue:
In Dynamics NAV 2013 ( I am not talking about R2!:) it is supported to use this property with NON-Primary key fields. I did not found any documentation about this. Also the current version MSDN is telling you a different story:
Anyway if you create a table relation in Dynamics NAV 2013 without using a Primary key field it is working:
Lets try this in NAV 2013
What happens if you are type in the name instead of select it? The system looks for the first records which meet the requirements and select it.
Ok my Item sample is not a real business scenario , but this means you have not do write code any longer if you want a table relation for a NON primary key field.
Thanks to Albert and Michaela for this great Info!