Как я могу получить данные из таблицы SQL в выпадающее поле datavalue

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SL	COURSE_CAT	          COURSECAT_ID
1	HEALTH & SAFETY	              1
2	FOOD & HYGIENE	              2
3	FIRST AID	                 3
4	FIRE SAFETY	                 4

SL	COURSE	         COURSE_ID	 COURSE_CODE
1	BB-GENTS	    1	           BBNTS
2	BB-LADIES	    1	           BBLDS
3	PIC-2 BARBER	    1	           PBRB
4	HSO-LABOUR ACC	    1	           HLBR
5	BASIC FOOD	    2	           BSFD
6	PIC-2 FOOD	    2	           PIFD
7	FIRST AID WORK	3	FIAD

Что я уже пробовал:

<asp:DropDownList ID="ddcoursecat" runat="server" Height="20px" Width="168px" OnSelectedIndexChanged="ddcoursecat_SelectedIndexChanged" AutoPostBack="True">
                                                  </asp:DropDownList>

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<asp:DropDownList ID="ddcourse" runat="server" Height="20px" Width="168px" AutoPostBack="True">
                                                    </asp:DropDownList>

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I have two dropdown control (Course_cat, course)
Course dd is getting populated from course table using Course_cat ID.
my intention is if a Course is selected its datavalue field should bind corresponding Course code from course_code column.
please help me to solve this.

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protected void ddcoursecat_SelectedIndexChanged(object sender, EventArgs e)
       {
               ddshift.Items.Insert(0, new ListItem("---SELECT---", "0"));
             //  ddcourse.Items.Insert(0, new ListItem("---SELECT---", "0"));
              // ddcourse.SelectedIndex = (0);
               try
               {
                   string CS = ConfigurationManager.ConnectionStrings["erpconnect"].ConnectionString;

                   using (SqlConnection con = new SqlConnection(CS))
                   {
                       SqlCommand cmd = new SqlCommand("SELECT  COURSE,COURSE_CODE from tbl_course WHERE COURSECAT_ID=" + ddcoursecat.SelectedValue +"", con);
                       {
                           if (ddcoursecat.SelectedIndex == 0)
                           {
                               ddcourse.Items.Insert(0, new ListItem("---SELECT---", "0"));
                          }
                           else
                           {

                               ddcourse.Items.Insert(0, new ListItem("---SELECT---", "0"));
                               con.Open();
                               ddcourse.DataSource = cmd.ExecuteReader();
                               ddcourse.DataTextField = "COURSE";
                               ddcourse.DataValueField = "COURSE_CODE";
                               ddcourse.DataBind();
                           }

                       }
                   }
               }
               catch
               {


               }

               finally
               {
                   this.Dispose();
               }

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