Question

I am trying to query data of a specific column text from another column.

Basically, I have a Supplier Database that has a SupplierID and Country column.

I already have the SupplierID for that specific row for example, it is 14. I would like to get the text value of Country column based on the 14 value.

The Supplier ID I am getting by the following code (listbox):

<asp:ListBox ID="SupplierListBox" runat="server" 
            DataSourceID="SupplierCompanyDataSource" DataTextField="Company" 
            DataValueField="SupplierID" Width="315px" 
            Height="80px" 
            onselectedindexchanged="SupplierListBox_SelectedIndexChanged" 
            AutoPostBack="True"></asp:ListBox>

Code:

        string SupplierListvalue = SupplierListBox.SelectedItem.Value; //SupplierListvalue retrieves the SupplierID value

        SqlDataReader rdr = null;
        SqlConnection conn = new SqlConnection("Data Source=localhost;Initial Catalog=ROG;Integrated Security=True");
        SqlCommand cmd = new SqlCommand("select Country from SupplierDB", conn);
        cmd.Connection = conn;

        conn.Open();
        rdr = cmd.ExecuteReader();
        while (rdr.Read())
        {
            TextBox1.Text = rdr["Country"].ToString();
            MessageBox.Show("Connection Successful");
            MessageBox.Show(rdr.ToString());
        }

        conn.Close();

Answer 1

Well, it’s not clear what’s the main problem, so i’ll show you a working example which selects the Country column from database with ADO.NET, uses Parameters to avoid SQL-Injection and using-statement to ensure that all unmanaged resources as the connection get disposed(closed).

string sql = @"
            SELECT Country
            FROM dbo.Supplier
            WHERE SupplierID = @SupplierId";
using (var con = new SqlConnection("Data Source=localhost;Initial Catalog=ROG;Integrated Security=True"))
{
    using (var cmd = new SqlCommand(sql, con))
    {
        con.Open();
        cmd.Parameters.Add("@SupplierId", SqlDbType.Int);
        cmd.Parameters["@SupplierId"].Value = int.Parse(SupplierListBox.SelectedItem.Value);
        using (var rdr = cmd.ExecuteReader())
        {
            if (rdr.Read())
            {
                TextBox1.Text = rdr.GetString(0);
            }
        }
    }
}