string connStr = "Server DSN=Demodata"; PsqlConnection conn = new PsqlConnection(connStr); try { conn.Open(); string sql = "select ID,First_Name,Last_Name from person order by id"; var cmd = new PsqlCommand(sql, conn); var adapter = new PsqlDataAdapter(cmd); var dt = new DataTable("Person"); adapter.Fill(dt); conn.Close(); dgv.DataSource = dt; // dgv = DataGridView } catch (PsqlException err) { Console.WriteLine(err.ToString()); }