Since I was not able to propose the result of a MySQL query in the default drop-down menu field type of CB (only values are possible), I decided to develop this useful (for me) plugin : EW dropdown SQL.

The plugin adds a field type to the fields definition of CB.
So the new field type 'Drop Down from MySQL Query' automaticallt adds a new field in the CB user profile. The field is a dropdown menu that displays the result of a personalized db query.
The result of the user selection is automatically stored in a new field of the CB user table.

Installation : add the plugin through the CB installation tools.

For CB 1.7 a change have to be done if you meet problem in Administrator User list (Save button and Pagination not working). Uninstall the plugin and reinstall the last version downloaded from that web site.