ASP.NET Connect SQL Server 2008

Step 1 สร้างเส้นทางเชื่อมต่อกับ SQL Server
public abstract class Global_class
    {
        public static string conn_str()
        {
           return "Data Source=ASUS-PC\\GHOSQLEXPRESS;Initial Catalog=agreeP2;Persist Security Info=True;User ID=sa;Password=1234";
         
        }
    }

Step 2 การเรียกใช้ข้อมูลใน SQL Server ให้มาแสดงใน Grid view

SqlConnection sql_conn = new SqlConnection(Global_class.conn_str());
sql_conn.Open();

 string strSQL;
            strSQL = "SELECT * FROM Product";

            SqlDataReader dtReader;
            sql_comm = new SqlCommand(strSQL, sql_conn);
            dtReader = sql_comm.ExecuteReader();

            GridView1.DataSource = dtReader;
            GridView1.DataBind();

            dtReader.Close();
            dtReader = null;

================================================
การเพิ่มข้อมูลเข้าไปใน Server

SqlConnection sql_conn = new SqlConnection(Global_class.conn_str());
            sql_conn.Open();
            SqlCommand insert_product = new SqlCommand("Insert Into Product (Product_Name) VALUES('" + TextBox1.Text + "')", sql_conn);
            insert_product.ExecuteNonQuery();
            sql_conn.Close();
================================================
การลบข้อมูลจาก Server

 SqlConnection sql_conn = new SqlConnection(Global_class.conn_str());
            sql_conn.Open();
            SqlCommand delete_p_b = new SqlCommand("Delete From Product_Branch where Product_ID = '" + DropDownList1.SelectedValue + "'", sql_conn);
            delete_p_b.ExecuteNonQuery();
            SqlCommand delete_p = new SqlCommand("Delete From Product where Product_ID = '" + DropDownList1.SelectedValue  + "'", sql_conn);
            delete_p.ExecuteNonQuery();
         
            sql_conn.Close();

=================================================
การใช้ DataTable

sql_conn = new SqlConnection(Global_class.conn_str());
                sql_conn.Open();

                SqlDataAdapter us = new SqlDataAdapter("select CAST(DATEPART(dd, Effitive) AS varchar(2)),CAST(DATEPART(mm, Effitive) AS varchar(2)),CAST(DATEPART(yyyy, Effitive) AS varchar(4)),CAST(DATEPART(dd, Renewal) AS varchar(2)),CAST(DATEPART(mm, Renewal) AS varchar(2)),CAST(DATEPART(yyyy, Renewal) AS varchar(4)) from Agreement where Agreement_ID = '" + Session["Agree_ID"] + "'", sql_conn);

                DataTable us_tb1 = new DataTable();
                us.Fill(us_tb1);
                Session["Day1"] = us_tb1.Rows[0][0].ToString();
                Session["Month1"] = us_tb1.Rows[0][1].ToString();
                Session["Year1"] = us_tb1.Rows[0][2].ToString();

                Session["Day2"] = us_tb1.Rows[0][3].ToString();
                Session["Month2"] = us_tb1.Rows[0][4].ToString();
                Session["Year2"] = us_tb1.Rows[0][5].ToString();
                sql_conn.Close();