<?php
    class classDatabase
    {
        protected static $instance = null;
        protected static $host = 'localhost';
        protected static $name = '';
        protected static $username = '';
        protected static $password = '';
        protected static $charset = 'UTF8';

        protected function __construct(){}
        protected function __clone(){}
        protected function __wakeup(){}

        final public static
        function getInstance() //this method can throw exception
        {
            if(is_null(static::$instance))
            {
                $dsn =
                    'mysql:host=' . static::$host .
                    ';dbname=' . static::$name .
                    ';charset=' . static::$charset;

                $options = array
                (
                    \PDO::ATTR_ERRMODE               => \PDO::ERRMODE_EXCEPTION,
                    \PDO::ATTR_DEFAULT_FETCH_MODE    => \PDO::FETCH_ASSOC,
                    \PDO::ATTR_TIMEOUT               => 4
                );

                static::$instance = new \PDO
                (
                    $dsn,
                    static::$username,
                    static::$password,
                    $options
                );
            }

            return static::$instance;
        }
    };

    try
    {
        $database = \saoDatabase::getInstance();

        $statement = $database->query
        ("
            SELECT `field`
            FROM `database`
            WHERE TRUE
                AND `condition`
            LIMIT 1;
        ");

        $fetched_field = $statement->fetchColumn();

        echo $fetched_field;
    }
    catch(\PDOException $exception)
    {
        echo 'SQL error occurred';
    }
?>