Andrew Nurse wrote All DotNetNuke modules connect to the SQL Server using the same user (as configured in the web.config). If your web.config file specifies Integrated Security, it is the user under which ASP.Net is running (usually "NT AUTHORITY\NETWORK SERVICE"), not the current DNN user, that will be authenticated with SQL Server.

Andrew Nurse wrote You can access the current DNN user's ID by using the @UserID parameter in your SQL Query. I'm not exactly sure how the Windows Authentication Provider works, but I believe that the username in the Users table for that user is the same as their Windows user name, so the following query should work (or at least point you in the right direction). SELECT Username FROM {oQ}Users WHERE UserID=@UserID

It worked!!
I am using Survey Module and would like to Create a report that can be viewed by users. Here is the SQL syntax that I would like to share with others. it maybe useful for someone else.

SELECT DISTINCT Users.DisplayName, Surveys.ViewOrder, Surveys.Question, SurveyOptions.OptionName
FROM         Surveys INNER JOIN
                      SurveyOptions ON Surveys.SurveyID = SurveyOptions.SurveyID INNER JOIN
                      SurveyResults ON SurveyOptions.SurveyOptionID = SurveyResults.SurveyOptionID INNER JOIN
                      Users ON SurveyResults.UserID = Users.UserID INNER JOIN
                      UserProfile ON Users.UserID = UserProfile.UserID
WHERE     (UserProfile.PropertyDefinitionID = 45) AND (NOT (Surveys.ViewOrder IN (1, 9))) AND (Users.UserID IN
                          (SELECT DISTINCT @UserID
                            FROM  Users ))

Many thanks again.