Question

i am using asp.net C# SQL to create a webpage.I need to list out a courseID to let user choose, but it list out two time same value in dropdownlist
S1111
S2222
S3333
S1111
S2222
S3333
,someone help

   protected void Page_Load(object sender, EventArgs e)
    {  
        SqlConnection conn;
        SqlDataReader dtr;
        SqlCommand cmd;

        string Connnection = ConfigurationManager.ConnectionStrings["ELearing"].ConnectionString;
        conn = new SqlConnection(Connnection);

        if (!Page.IsPostBack)
        {
            //Get Staff Information
            conn.Open();
            string cmdString = "SELECT DISTINCT CourseID FROM Schedule WHERE(StaffID = @scheduleStaffID)";
            cmd = new SqlCommand(cmdString, conn);
            cmd.Parameters.AddWithValue("@scheduleStaffID", Session["UserID"].ToString());

            dtr = cmd.ExecuteReader();

            while (dtr.Read())
            {
                ddlCourse.Items.Add(dtr["CourseID"].ToString());
            }
            dtr.Close();
            conn.Close();
        }
    }

Answer 1

Try these

1.Do you get duplicates when you do externally SELECT DISTINCT CourseID FROM Schedule WHERE StaffId = 1

2.use breakpoints to check additional post backs.

3.Try ddlCourse.Items.Clear just before your while loop.