Suppliers Registration Fields

Hi,

This is my first question in this Community, I have started with SAP Sourcing recently.

In SAP Sourcing, the field External ID in Suppliers Registration is unique, a primary key, so I can´t register two Suppliers with the some number, SAP Sourcing gives me a red advice, it makes sense.

I would like to know if the field Tax ID, can have this characteristic too and how can I do it in SAP Sourcing. I don´t want the system to allow me to register two Suppliers with the same Tax ID.

Can it be done in other fields too?

Would this rule also be applied when Suppliers are registering through Self-Registration link? Would it be possible for them to get a red alert saying "This Tax ID is already registered in XXX Company SAP Sourcing"?

Thank you very much!

Best Regards,

Eugénio