Aggregate Function of Sum

private void button1_Click(object sender, EventArgs e)
        {
            /*code for insert a new record in table pembelian*/
            perintahsql = new SqlCeCommand("INSERT INTO pembelian (kd_barang, nama, jumlah) VALUES (@kd_barang,  @nama, @jumlah)", koneksi);
            perintahsql.Parameters.AddWithValue("@kd_barang", textBox1.Text);
            perintahsql.Parameters.AddWithValue("@nama", textBox2.Text);
            perintahsql.Parameters.AddWithValue("@jumlah", textBox3.Text);

            koneksi.Open();
            perintahsql.ExecuteNonQuery();
            koneksi.Close();
            pembelian();

            /*get the sum from column jumlah in table pembelian where kd_barang = 111*/
            string beli;
            perintahsql = new SqlCeCommand("SELECT SUM(jumlah) as beli FROM pembelian WHERE kd_barang = 111", koneksi);
            koneksi.Open();
            beli = perintahsql.ExecuteScalar().ToString();
            koneksi.Close();
            MessageBox.Show(beli);

            /*get the sum from column jumlah in table gudang where kd_barang = 111*/
            string gudang_total;
            perintahsql = new SqlCeCommand("SELECT SUM(jumlah) as gudang FROM gudang WHERE kd_barang = 111", koneksi);
            koneksi.Open();
            gudang_total = perintahsql.ExecuteScalar().ToString();
            koneksi.Close();
            int total = int.Parse(beli) + int.Parse(gudang_total);

            /*update table gudang where kd_barang = 111 after insertion in table pembelian*/
            perintahsql = new SqlCeCommand("UPDATE gudang SET nama = 'karet', jumlah = " + total.ToString() + " WHERE kd_barang = 111", koneksi);
            koneksi.Open();
            perintahsql.ExecuteNonQuery();
            koneksi.Close();
            MessageBox.Show(total.ToString());
            gudang();
        }