Pqxx demo 1

#include <iostream>
#include <pqxx/pqxx>

int main()
try
{
  // using namespace pqxx; 
  
  // spojeni s DB "dbname=sqlquiz host=localhost user=aaa password=bbb"
  pqxx::connection conn("dbname=test");

  // transakce
  pqxx::work tran(conn, "demo-transaction");     
  
  // sql prikazy
  pqxx::result r1(tran.exec("SET search_path TO pokus;"));
  pqxx::result r2(tran.exec("INSERT into abc (x, y) "
                    "  SELECT coalesce(max(x),0)+1, random() FROM abc ;"));
  pqxx::result r3(tran.exec("SELECT * FROM abc;"));

  // pruchod vyslednou tabulkou
  if (r3.empty()) 
    std::cout << "tabulka je prazdna\n";
  else
    std::cout << "tabulka ma " 
              << r3.columns() << " sloupce a "
              << r3.size()    << " radku\n\n";

  for (pqxx::result::const_iterator i=r3.begin(); i!=r3.end(); ++i)
    {
      // sloupce muzeme adresovat absolutne nebo jmenem
      std::cout << "x = " << i[0].as(std::string()) << "   "
                << "y = " << i["y"].as(double())
                << std::endl;
    }

  // commit transakce, neni nutny pokud pracujeme pouze se selekty
  tran.commit();
}
catch(...)
{
  std::cerr << "demo : exception ...\n";
}