How can I retrieve data from one column refer to another two columns from the same table ?

// Find the Employee and display it in the List Box
        private void btnFindFlightId_Click(object sender, System.EventArgs e)
        {
            SqlDataReader rdr = null;
            SqlConnection con = null;
            SqlCommand cmd = null;
            int flightId = 0;
            try
            {
                // Open connection to the database
                string ConnectionString = "server=YourServerName;uid=UserName;"+
                    "pwd=Password; database=YourDatabaseName"; // Use your database connection here.
                con = new SqlConnection(ConnectionString);
                con.Open();
                // Set up a command with the given query and associate
                // this with the current connection.
                string CommandText = "SELECT Flight_Id" +
                                     "  FROM Flight_Info" +
                                     " WHERE (depart_from = @depart)" +
                                     " AND destination = @destination";
                cmd = new SqlCommand(CommandText);
                cmd.Connection = con;
                // Add LastName to the above defined paramter @Find
                cmd.Parameters.Add(
                    new SqlParameter(
                    "@depart", // The name of the parameter to map
                    System.Data.SqlDbType.VarChar, // SqlDbType values
                    20, // The width of the parameter
                    "Depart"));  // The name of the source column

                cmd.Parameters.Add(
                    new SqlParameter(
                    "@destination", // The name of the parameter to map
                    System.Data.SqlDbType.VarChar, 
                    20, // The width of the parameter
                    "Destination"));  
                // Fill the parameter with the value retrieved
                // from the text field
                cmd.Parameters["@depart"].Value = txtDepart.Text; // This is the input field. 
                cmd.Parameters["@destination"].Value = txtDestination.Text; // This is the input field. 
                // Execute the query
                rdr = cmd.ExecuteReader();
                while(rdr.Read())
                {
                    flightId = Convert.ToInt32(rdr[Flight_Id]);// you can write your own way of using flight id further 
                }
            }
            catch(Exception ex)
            {
                // error message
                throw(ex.Message);
            }
            finally
            {
                // Close data reader object and database connection
                if (rdr != null)
                    rdr.Close();
                if (con.State == ConnectionState.Open)
                    con.Close();
            }
        }
    }