public void Export_Click(object sender, EventArgs e)
{
        string sqlString = "server=.\\SQL2005;database=stu_info;uid=sa;pwd=123456";
        try
        {
            SqlConnection sqlconn = new SqlConnection(sqlString);
            sqlconn.Open();
            string sql = "SELECT A.id,A.name,B.title FROM person AS A JOIN book AS B ON A.id=B.id";
            SqlCommand cmd = new SqlCommand(sql, sqlconn);
            SqlDataReader reader = cmd.ExecuteReader();
            string insql;
            while (reader.Read())
            {
                insql = "INSERT INTO lh VALUES('" + reader[0] + "','" + reader[1] + "','" + reader[2] + "')";
                SqlCommand incmd = new SqlCommand(sql, sqlconn);
                incmd.ExecuteNonQuery();
            }
        }
        catch (SqlException ex)
        {
            string MsgEx = ex.Message;
            MsgExport.Visible = true;
            MsgExport.Text = MsgEx;
        }
    }

incmd.ExecuteNonQuery();

        string sqlString = "server=.\\SQL2005;database=stu_info;uid=sa;pwd=123456";
        using(SqlConnection sqlconn = new SqlConnection(sqlString))
        using(SqlConnection sqlconn2 = new SqlConnection(sqlString))
        {
            sqlconn.Open();
            sqlconn2.Open();
            string sql = "SELECT A.id,A.name,B.title FROM person AS A JOIN book AS B ON A.id=B.id";
            SqlCommand cmd = new SqlCommand(sql, sqlconn);
            SqlDataReader reader = cmd.ExecuteReader();
            string insql;
            SqlCommand incmd = sqlconn2.CreateCommand();
            while (reader.Read())
            {
                insql = "INSERT INTO lh VALUES('" + reader[0] + "','" + reader[1] + "','" + reader[2] + "')";
                incmd.CommandText= insql;
                incmd.ExecuteNonQuery();
            }
        }