C#

using System.Data;
using System.Windows.Forms;
using Npgsql;

class Form1 : Form
{
    static void Main()
    {
            Application.Run(new Form1());
    }

    DataGridView dataGridView1 = new DataGridView();

    Form1()
    {
        string s = "SERVER=localhost;USER=postgres";
        string query = @"select * from pg_tables";
        var con1 = new NpgsqlConnection(s);
        IDbCommand cmd = con1.CreateCommand();
        cmd.CommandText = query;
        con1.Open();
        var dr = cmd.ExecuteReader();
        dataGridView1.DataSource = dr;
        Controls.Add(this.dataGridView1);
    }

}