Customized lookup in Report Dialog box

Hai experts !!

I would like to  implement Customized lookup in Report Dialog box in Ax2009.

for example i have one field(dlgStudentid ) in report dialog.

I have written like this in the dialog method

public Object dialog(Object _dialog)

{

   DialogRunbase dialog = _dialog;

    ;

    dlgStudentid  = dialog.addField(typeid(Studentid ))

    return dialog;

}

In the above Studentid ---edt which has relation  with the field(StudentId)

 in the table StudentTable .

 In the StudentTable we have duplicate records with StudentId as StudentId is not unique in this table.

So when we are running the report in the dialog prompt its showing duplicate records

i.e  StudentId 401

                         401

                         402

                         402

Here we wish to display records uniquely.

like  StudentId 401

                          402

Could you please suggest me how could I achieve this

Regards,

Krishna