.net gridview button按钮不执行操作

protected void GridView1_SelectedIndexChanged(object sender, EventArgs e)
{
string c = Session ["cid"] as string ;

    string constr = "Data Source=.;Initial Catalog=MEAL;Integrated Security=True";
    SqlConnection conn = new SqlConnection(constr);
    conn.Open();
    string sq1 = "update [orders]  set Ostatus='3'  cid='" + c + "'";

    SqlCommand cmd = new SqlCommand(sq1, conn);
    cmd = new SqlCommand(sq1, conn);
    cmd.ExecuteNonQuery();
    conn.Close();

}


    点击button按钮后，当行数据的ostatus状态改为3，但是点击之后并没有执行代码，各位大神看看是哪里出问题啦