1. This is not the right forum for your question, as the client API deals with controls, that are executed on the client computer.
2. the User Information is currently handled by the asp.Net Membership component, that stores this information in a proprietary format within a single field (aspnet_Profile.PropertyValueString). Instead of trying to access these fields with SQL, you should use the membership provider interface.
3. Note, that there will be major enhancements in this area in DNN 3.3/4.1. Read the latest Blog Entries from Charles Nurse for further details.