i h ave wrote this code to get the details of employee based on employer id. but getting error that invalid column name of employeerid

protected void Button1_Click(object sender, EventArgs e)
    {
        string strConnection = ConfigurationManager.ConnectionStrings["MyConsString"].ConnectionString;
        SqlConnection conn = new SqlConnection(strConnection);
        SqlCommand cmd = new SqlCommand("Select * from Employeertable INNER JOIN Employeetable on Employeertable.Employeerid= Employeetable.Employeerid where Employeertable.Employeerid=" + DropDownList1.SelectedItem.ToString() + "", conn);
        conn.Open();
        cmd.ExecuteNonQuery();
        SqlDataAdapter da = new SqlDataAdapter(cmd);
        DataSet ds = new DataSet();
        da.Fill(ds);
        GridView1.DataSource = ds;
        GridView1.DataBind();
        conn.Close();

    }
}