如何给数据库发请求

Question

    string connectionstring = "Data Source=CE5BC36663C4490\\SQLEXPRESS;Initial Catalog=sql;Integrated Security=True";        SqlConnection conn = new SqlConnection(connectionstring);        string str = "select * from dept";        //SqlCommand cmd = new SqlCommand(str,conn );        SqlDataAdapter da = new SqlDataAdapter();        da.TableMappings.Add("Table","dept");        da.SelectCommand = new SqlCommand(str, conn);       DataTable  dt = new DataTable ("dept");       da.Fill(dt );               dt.AcceptChanges();        dt.Rows [1].Delete ();                       //dt.RejectChanges();        //da.Update(dt);        dt.AcceptChanges();               GridView1.DataSource = dt;        GridView1.DataBind();这样做 只是内存 删除，数据库中的数据仍然存在！如何给数据库发请求删除第一行呢