Function check on field registration client

[intech6tem]

Hello,

I wish to assign to an additionnal field of the client registration form, a function checking if the input value exists in the Joomla! DataBase.

The goal is to when the client wanting to register can only do it by using a valid ID (ID transmitted by the sponsorship thus corresponding to the ID of a sponsor - Joomla user table).

I didn't find any option in the GUI allowing me to reach my goal and I didn't find yet a PHP files to modify.

VirtueMart version : 2.6.6
Joomla! version : 2.5.22

Thank you in advance.

Clément.

PS: I am sorry for my bad english, it isn't my native language. Have a nice day !