In this article I will explain how to bind / fill / populate data to DropDownList control from database records in ASP.Net using C# and VB.Net.
The data will be populated from database table using DataReader. 
I have made use of the following table Customers with the schema as follows.
Bind / Fill / Populate DropDownList control from database in ASP.Net using C# and VB.Net
I have already inserted few records in the table.
Bind / Fill / Populate DropDownList control from database in ASP.Net using C# and VB.Net
Note: You can download the database table SQL by clicking the download link below.
          Download SQL file
HTML Markup
The HTML Markup consists of an ASP.Net DropDownList which will be populated from database.
<asp:DropDownList ID = "ddlCustomers" runat="server">
You will need to import the following namespaces.
using System.Data;
using System.Configuration;
using System.Data.SqlClient;
Imports System.Data
Imports System.Configuration
Imports System.Data.SqlClient
Populating DropDownList control from database in ASP.Net
Inside the Page Load event of the page, the DropDownList is populated with the records of the Customers Table.
The CustomerId and the Name column values are fetched from the database using SqlDataReader and are assigned to the DataTextField and DataValueField properties of the DropDownList control.
DataTextField – The values of the Column set as DataTextField are visible to the user.
DataValueField – The values of the Column set as DataValueField are not visible to the user. Generally ID or Primary Key columns are set as values in order to uniquely identify a DropDownList Item.
Once the records from database are populated, a default item is inserted at the first position.
protected void Page_Load(object sender, EventArgs e)
    if (!this.IsPostBack)
        string constr = ConfigurationManager.ConnectionStrings["constr"].ConnectionString;
        using (SqlConnection con = new SqlConnection(constr))
            using (SqlCommand cmd = new SqlCommand("SELECT CustomerId, Name FROM Customers"))
                cmd.CommandType = CommandType.Text;
                cmd.Connection = con;
                ddlCustomers.DataSource = cmd.ExecuteReader();
                ddlCustomers.DataTextField = "Name";
                ddlCustomers.DataValueField = "CustomerId";
        ddlCustomers.Items.Insert(0, new ListItem("--Select Customer--", "0"));
Protected Sub Page_Load(sender As Object, e As EventArgs) Handles Me.Load
    If Not Me.IsPostBack Then
        Dim constr As String = ConfigurationManager.ConnectionStrings("constr").ConnectionString
        Using con As New SqlConnection(constr)
            Using cmd As New SqlCommand("SELECT CustomerId, Name FROM Customers")
                cmd.CommandType = CommandType.Text
                cmd.Connection = con
                ddlCustomers.DataSource = cmd.ExecuteReader()
                ddlCustomers.DataTextField = "Name"
                ddlCustomers.DataValueField = "CustomerId"
            End Using
        End Using
        ddlCustomers.Items.Insert(0, New ListItem("--Select Customer--", "0"))
    End If
End Sub
Bind / Fill / Populate DropDownList control from database in ASP.Net using C# and VB.Net