DataSet和DataTable區別  
 da.Fill(ds, "alias_1");                            //使用DataAdapter的Fill方法(填充)，調用SELECT命令，別名       
 dataGridView8.DataSource = ds.Tables[0];

 da.Fill(dt);       //直接填充給dt
 flex.DataSource = dt;
 
 ds.Tables[0]==dt
 DateSet是數據在內存中的緩存，是保存數據的數據結構，相當於一個虛擬的數據庫，他可以包含多個DateTable
 好像winform裏面綁定只能綁定dataTable
 簡單而言,dataset和datatable都是ADO的非連接層,dataset是一個位於內存中表示外部數據的對象，它是一個類型，該類型維護三個內部強類型集合，其中包括了datatablecollection,  dataset的tables屬性能夠訪問包含多個datatable的datatablecollection


 










        
 
private void button1_Click(object sender, EventArgs e)
        {
            SqlConnection conn = new SqlConnection("server=.;database=DB_JXC;uid=sa;pwd=PSWD123");
            conn.Open();
            if (conn.State==ConnectionState.Open)
            {
                label1.Text = "數控庫已經連接並打開
 
";
            }
        }


        private void button2_Click(object sender, EventArgs e)
        {
            SqlConnection conn = new SqlConnection("server=.;database=DB_JXC;uid=sa;pwd=PSWD123");
            conn.Open();
            if (conn.State == ConnectionState.Open)
            {
                label2.Text 
 
= "數控庫已經連接並打開";
            }

            conn.Close();
            if (conn.State==ConnectionState.Closed)
            {
                label2.Text = "數控打開後又關閉了";
            }
        }


        private void button3_Click(object sender, EventArgs e)
        {
            SqlConnection conn = new SqlConnection("server=.;database=DB_JXC;uid=sa;pwd=PSWD123");
            conn.Open();
            if (conn.State == ConnectionState.Open)
            {
                label3.Text = "數控庫已經連接並打開";
            }

            conn.Dispose();
            label3.Text = "conn.Dispose()";            
        }

        private void button4_Click(object sender, EventArgs e)
        {
            SqlConnection conn = new SqlConnection("server=.;database=DB_JXC;uid=sa;pwd=PSWD123");
            conn.Open();
            if (conn.State == ConnectionState.Open)
            {
                label4.Text = "數控庫已經連接並打開";
            }

            SqlCommand cmd = new SqlCommand();
            cmd.Connection = conn;
            cmd.CommandText = "select count(*) from khxjd";
            cmd.CommandType = CommandType.Text;

            int i = Convert.ToInt32(cmd.ExecuteScalar());
            label4.Text = "表中有" + i.ToString() + "條記錄！";

        }

        private void button5_Click(object sender, EventArgs e)
        {
            SqlConnection conn = new SqlConnection("server=.;database=DB_JXC;uid=sa;pwd=PSWD123");
            conn.Open();
            if (conn.State == ConnectionState.Open)
            {
                label5.Text = "數控庫已經連接並打開";
            }

            SqlCommand cmd = new SqlCommand();
            cmd.Connection = conn;
            cmd.CommandText = "update khxjd set qty=100+isnull(qty,0)";
            cmd.CommandType = CommandType.Text;

            int i = Convert.ToInt32(cmd.ExecuteNonQuery());
            label5.Text = "更新了表中" + i.ToString() + "條記錄！";
        }


        //sqlDataReader,是向前的。
        //針對於一個sqlConnection,創建多個sqlDataReader,要先關閉上一個sqlDataReader，才能使用下一個sqlDataReader.

        private void button6_Click(object sender, EventArgs e)
        {
            SqlConnection conn = new SqlConnection("server=.;database=DB_JXC;uid=sa;pwd=PSWD123");
            conn.Open();
            if (conn.State == ConnectionState.Open)
            {
                label6.Text = "數控庫已經連接並打開";
            }

            SqlCommand cmd = new SqlCommand();
            cmd.Connection = conn;
            cmd.CommandText = "select top 5 khxjdh,itm,nsn,prd_name_eng,prd_name_chs,qty from khxjd";
            cmd.CommandType = CommandType.Text;
                        
            SqlDataReader sdr= cmd.ExecuteReader();
            while (sdr.Read())
            {
                label6.Text = label6.Text   + "," + sdr[1].ToString();
            }

            label6.Text = label6.Text + "。讀取完成！";


        }

        private void button7_Click(object sender, EventArgs e)
        {
            SqlConnection conn = new SqlConnection("server=.;database=DB_JXC;uid=sa;pwd=PSWD123");
            conn.Open();
            if (conn.State == ConnectionState.Open)
            {
                label7.Text = "數控庫已經連接並打開";
            }

            SqlCommand cmd = new SqlCommand();
            cmd.Connection = conn;
            cmd.CommandText = "select top 5 khxjdh,itm,nsn,prd_name_eng,prd_name_chs,qty from khxjd";
            cmd.CommandType = CommandType.Text;

            SqlDataReader sdr = cmd.ExecuteReader();
            if (sdr.HasRows) 
            {
                label7.Text = "有數據";
            }
            else
            {
                label7.Text = "無數據";
            }

            sdr.Close(); 

        }


        //SqlDataAdapter:DataAdapter對象在DataSet與數據之間起橋梁作用
        private void button8_Click(object sender, EventArgs e)
        {
            SqlConnection conn = new SqlConnection("server=.;database=DB_JXC;uid=sa;pwd=PSWD123");

            //conn.Open();     //說明一下：使用 SqlDataAdapter時，只要SqlConnection有效就行，不需要 打開！！！

            if (conn.State == ConnectionState.Open)
            {
                label8.Text = "數控庫已經連接並打開";
            }
            else
            {
                label8.Text = "數控庫還未打開";  //ok
            }

            //SqlCommand cmd = new SqlCommand();
            //cmd.Connection = conn;            
            //SqlCommand cmd = new SqlCommand( "select top 5 khxjdh,itm,nsn,prd_name_eng,prd_name_chs,qty from khxjd",conn);           
            //SqlDataAdapter da = new SqlDataAdapter();
            //da.SelectCommand = cmd;

            //DataSet ds = new DataSet();
            // da.Fill(ds, "alias_1");                         //使用DataAdapter的Fill方法(填充)，調用SELECT命令，別名
            //dataGridView8.DataSource = ds.Tables[0];

            


            SqlDataAdapter da = new SqlDataAdapter("select top 5 khxjdh,itm,nsn,prd_name_eng,prd_name_chs,qty from khxjd", conn); //創建DataAdapter數據適配器實例

            if (conn.State == ConnectionState.Open)
            {
                label8.Text = label8.Text+ "2.數控庫已經連接並打開";
            }
            else
            {
                label8.Text = label8.Text + "2.數控庫還未打開";  //ok
            }

            DataSet ds = new DataSet();                        //創建DataSet實例
            da.Fill(ds, "alias_1");                            //使用DataAdapter的Fill方法(填充)，調用SELECT命令，別名       
            dataGridView8.DataSource = ds.Tables[0];
            
            //label8.Text = "數控查詢完成";

            if (conn.State == ConnectionState.Open)
            {
                label8.Text = label8.Text + "3.數控庫已經連接並打開";
            }
            else
            {
                label8.Text = label8.Text + "3.數控庫還未打開";  //ok
            }

            //conn.Close();                                      //關閉數據庫            
        }


// load table from db
string sql = "select * from products";
string conn = GetConnectionString();
System.Data.OleDb.OleDbDataAdapter da = new System.Data.OleDb.OleDbDataAdapter(sql, conn);


DataTable dt = new DataTable();
da.Fill(dt);       //直接填充給dt

// bind to grid
_flex.Cols[0].Width = 20;
_flex.ShowCursor = true;
_flex.DataSource = dt;

// add calculated field
dt.Columns.Add("ValueInStock", typeof(decimal), "UnitPrice * UnitsInStock");
_flex.Cols["ValueInStock"].Format = "c";

// add unbound column
Column col = _flex.Cols.Add();
col.Name = col.Caption = "Unbound";

DataSet和DataTable區別，Connection、Command、DataReader、DataAdapter、DataSet