winfrom SQL server 控件Listbox 输出数据表中的所有行和指定列

private void btnConn_Click(object sender, EventArgs e)
{
//定义连接字符串
string constr = "server=192.168.1.1;database=**OA;uid=***;pwd=***;";
SqlConnection con = new SqlConnection(constr);
try
{
con.Open();
SqlCommand cmd = new SqlCommand("select * from ERPUser", con);
SqlDataReader dr = cmd.ExecuteReader();
while (dr.Read())
{
listBox1.Items.Add(dr.GetValue(0) + "  " + dr.GetValue(1) + " " + dr.GetValue(3));

}
dr.Close();

}
catch (Exception exc)
{
MessageBox.Show(exc.Message);
}
finally
{
con.Close();
}
}

private void btnClear_Click(object sender, EventArgs e)
{
listBox1.Items.Clear();
}