サンプルコード 1

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());
}