Accessing vBulletin Membership Data

[MacroPhotoPro]

I have an independent database application, within a custom vBulletin page, which accesses a separate database table. Yet I am trying to integrate the vBulletin membership names to this custom table. When I, as the administrator, attempt to work with this data table, while logged into vBulletin, I get the following error message:

It is trying to use the vBulletin Member ID as a foreign key. How do I access this data? What is the datatype? This data must be stored in the session somehow, since vBulletin knows persistently when the active user is logged in or not, etc.

Any help in how to access and integrate this information into my custom data table would be much appreciated.

Jack