how to display the value of the column in drop down list

i need to show the selected value from database in drop down list and this drop down list contains items on of them is the selected one from database

asp.net code
"DropDownList3" runat="server" EnableViewState="true" DataSourceID="SqlDataSource7" AppendDataBoundItems="true" DataTextField="Name" DataValueField="SId" Width="130px" Height="25px"> Select School
"SqlDataSource7" runat="server" ConnectionString="<%$ ConnectionStrings:ConnectionString %>" SelectCommand="SELECT [SId],[Name] FROM [School]">
SqlDataReader myReader = null;
SqlCommand query = new SqlCommand(@"select * from dbo.Cousres INNER JOIN dbo.School ON
dbo.School.SId=dbo.Cousres.SId where dbo.Cousres.CourseId='" + TextBox7.Text + "'", conn);
SqlDataAdapter da = new SqlDataAdapter();
myReader = query.ExecuteReader();
while (myReader.Read())
{
TextBox3.Text = (myReader["CourseId"].ToString());
TextBox4.Text = (myReader["CousreName"].ToString());
DropDownList3.SelectedValue= (myReader["Name"].ToString());
Edit.Visible = false;
}

please help

thnak you