<pre>using System;
using System.Data;
using System.Data.SqlClient;
using System.Windows.Forms;

namespace Northwind_Sql_Data_Extraction
{
    public partial class Form1: Form
    {
        public Form1()
        {
            InitializeComponent();
        }

        private void Form1_Load(object sender, EventArgs e)
        {
            // TODO: This line of code loads data into the 'northwindDataSet.Customers' table. You can move, or remove it, as needed.
            this.customersTableAdapter.Fill(this.northwindDataSet.Customers);
            // TODO: This line of code loads data into the 'northwindDataSet.Order_Details' table. You can move, or remove it, as needed.
            this.order_DetailsTableAdapter.Fill(this.northwindDataSet.Order_Details);
            // TODO: This line of code loads data into the 'northwindDataSet.Orders' table. You can move, or remove it, as needed.
            this.ordersTableAdapter.Fill(this.northwindDataSet.Orders);        
        }

        private void FunctionThree()
        {
            using (SqlConnection con = new SqlConnection("Data Source=LAPTOP- CI6IN3IA\\SQLEXPRESS;Initial Catalog=Northwind;Integrated Security=True"))
            {
               {
                    con.Open();
             string AddColumn = "ALTER TABLE[Order Details] ADD[Order Details Value] int";
                    SqlCommand sql = new SqlCommand(AddColumn, con);
                    sql.ExecuteNonQuery();
                }
                catch (Exception ex)
                {
                    MessageBox.Show("order detail value already created",ex.Message);
                }
                try
                {
                    string UpdateValue = "UPDATE [Order Details] SET [Order Details].[Order Details Value] = ([Order Details].Quantity * [Order Details].UnitPrice)";
                    SqlCommand insertCommand = new SqlCommand(UpdateValue, con);
                    insertCommand.ExecuteNonQuery();
                    con.Close();
                }
                catch (Exception ex)
                {
                    MessageBox.Show(ex.Message);
                }
            }
        }

        private void Button1_Click(object sender, EventArgs e)
        {
            switch (comboBox1.SelectedItem.ToString())
            {
                case "Task 3":
                    FunctionThree();                   
                    break;
                default:
                    MessageBox.Show("Please select a value between 1 and 5");
                    break;
            }
        }
    }
}

What I have tried:

I'm trying to make my code for adding a new column to a table more streamlined. Although my method works, I receive an exception error indicating that the table produced must be unique. Obviously, this is due to the fact that Sql.ExecuteNonQuery causes the table to be recreated if I run the code several times, but I can't seem to find a viable solution.