ถามเรื่องของ DataBase หน่อยครับเกี่ยวกับ sql ผมยังงงๆ

using System;
using System.Collections.Generic;
using System.ComponentModel;
using System.Data;
using System.Drawing;
using System.Linq;
using System.Text;
using System.Windows.Forms;
using System.Data;
using System.Data.SqlClient;

namespace Pharmacy
{
    
    public partial class Form1 : Form
    {
        public DateTime dt = new DateTime(DateTime.Now.Ticks);
        private DataSet data;
        private SqlConnection connection;
        public Form1()
        {
            InitializeComponent();
            textBox1.Text = Convert.ToString(dt.ToLongDateString());
        }
        private void Form1_Load(object sender, EventArgs e)
        {
            string conStr = @"Data Source=.\SQLEXPRESS;
                            AttachDbFileNmae=|DataDirectory|Pharmacy.mdf;
                            Integrated Security=True;User Instance=True;";
            connection = new SqlConnection(conStr);
            
            data = new DataSet();
            string sql = "SELECT ชื่อการค้า FROM Pharmacy";
            SqlCommand command = new SqlCommand(sql,connection);
            SqlDataAdapter adapter = new SqlDataAdapter(command);
            adapter.Fill(data, "pha");

            sql = "SELECT ขาย FROM Pharmacy";
            command.CommandText = sql;
            adapter.SelectCommand = command;
            adapter.Fill(data, "phar");
            connection.Close();
        
        }

        private void button1_Click(object sender, EventArgs e)
        {
            listBox1.Items.Clear();
            string d;
            for (int i = 0; i < data.Tables["pha"].Rows.Count; i++)
            {
                d = data.Tables["pha"].Rows[i][0].ToString();
                listBox1.Items.Add(d);
            }
        }