title: The variable name '@VarName' has already been declared Issue
body: <p>I am inserting multiple items into table based on a selection from drop down list.  When I select one item from the drop down then everything works fine but when I select multiple items then I get this error</p>
  
  <pre><code>The variable name '@CompName' has already been declared. Variable names must be unique within a query batch or stored procedure.
  </code></pre>
  
  <p>what am i doing wrong?  thanks
  here is my code</p>
  
  <pre><code>protected void DV_Test_ItemInserting(object sender, DetailsViewInsertEventArgs e)
      {
          foreach (ListItem listItem in cblCustomerList.Items)
          {
              if (listItem.Selected)
              {
                  string Name= listItem.Value;
                  sqlcon.Open();
                  string CompName= ((TextBox)DV_Test.FindControl("txtCompName")).Text.ToString();
                  string Num = ((TextBox)DV_Test.FindControl("txtNum")).Text.ToString();
                  SqlCommand cmd = new SqlCommand("select CompNamefrom MyTable where CompName= '" + CompName+ "' and Num = '" + Num + "' and Name= '" + Name+ "'    ", sqlcon);
                  SqlDataReader dr = cmd.ExecuteReader();
                  if (dr.Read())
                  {
                      lblmsg.Text = "Not Valid";
                  }
                  else
                  {
                      dr.Close();
  
                      sqlcmd.CommandText = "INSERT INTO MyTable(CompName, Num, Name) VALUES(@CompName, @Num, @Name)";
                      sqlcmd.Parameters.Add("@CompName", SqlDbType.VarChar).Value = CompName;
                      sqlcmd.Parameters.Add("@Num", SqlDbType.VarChar).Value = Num;
                      sqlcmd.Connection = sqlcon;                 
                      sqlcmd.ExecuteNonQuery();
                      DV_Test.ChangeMode(DetailsViewMode.Insert);
                      sqlcon.Close();
                  }
                  sqlcon.Close();               
              }
  
           }
   }
  </code></pre>