Singleton для PDO. Установка режима выборки по умолчанию в FETCH_ASSOC. Исключения при ошибках. Пара вспомогательных функций.

<?php
function db(){
  static $db = null;
  if(is_null($db)){
    $db = new PDO('mysql:host=localhost;dbname=test', 'user', 'PaSsWoRd');
    $db->setAttribute(PDO::ATTR_ERRMODE, PDO::ERRMODE_EXCEPTION);
    $db->setAttribute(PDO::ATTR_DEFAULT_FETCH_MODE, PDO::FETCH_ASSOC);
    $db->query('set names utf8');
  }
  return $db;
}
function q($t){
  return db()->quote($t);
}
function query($q){
  return db()->query($q);
}
function one($q){
  return query($q)->fetch();
}
function all($q){
  return query($q)->fetchAll();
}

<?php
try {
    $dbh = new PDO('mysql:host=localhost;dbname=test', $user, $pass);
    foreach($dbh->query('SELECT * from FOO') as $row) {
        print_r($row);
    }
    $dbh = null;
} catch (PDOException $e) {
    print "Error!: " . $e->getMessage() . "<br/>";
    die();
}
?>

Экранировать строку для использования её в sql запросе

<?php
$conn = new PDO('sqlite:/home/lynn/music.sql3');

/* Simple string */
$string = 'Nice';
print "Unquoted string: $string\n";
print "Quoted string: " . $conn->quote($string) . "\n";
?>
Unquoted string: Nice
Quoted string: 'Nice'

<?php
$sth = $dbh->prepare("SELECT name, colour FROM fruit");
$sth->execute();

/* Fetch all of the remaining rows in the result set */
print("Fetch all of the remaining rows in the result set:\n");
$result = $sth->fetchAll();
print_r($result);
?>
Fetch all of the remaining rows in the result set:
Array
(
    [0] => Array
        (
            [NAME] => pear
            [0] => pear
            [COLOUR] => green
            [1] => green
        )

    [1] => Array
        (
            [NAME] => watermelon
            [0] => watermelon
            [COLOUR] => pink
            [1] => pink
        )

)

<?php
$sth = $dbh->prepare("SELECT name, colour FROM fruit");
$sth->execute();

/* Fetch the first column from the next row in the result set */
print("Fetch the first column from the next row in the result set:\n");
$result = $sth->fetchColumn();
print("name = $result\n");

print("Fetch the second column from the next row in the result set:\n");
$result = $sth->fetchColumn(1);
print("colour = $result\n");
?>
Fetch the first column from the next row in the result set:
name = lemon
Fetch the second column from the next row in the result set:
colour = red

<?php
/* Execute a prepared statement by passing an array of values */
$sql = 'SELECT name, colour, calories
    FROM fruit
    WHERE calories < :calories AND colour = :colour';
$sth = $dbh->prepare($sql, array(PDO::ATTR_CURSOR => PDO::CURSOR_FWDONLY));
$sth->execute(array(':calories' => 150, ':colour' => 'red'));
$red = $sth->fetchAll();
$sth->execute(array('calories' => 175, 'colour' => 'yellow'));
$yellow = $sth->fetchAll();
?>

<?php
/* Execute a prepared statement by passing an array of values */
$sth = $dbh->prepare('SELECT name, colour, calories
    FROM fruit
    WHERE calories < ? AND colour = ?');
$sth->execute(array(150, 'red'));
$red = $sth->fetchAll();
$sth->execute(array(175, 'yellow'));
$yellow = $sth->fetchAll();
?>

<?php
// Заставить pdo выбрасывать исключения при ошибках
$dbh = new PDO($conn, $user, $pwd);
$dbh->setAttribute(PDO::ATTR_ERRMODE, PDO::ERRMODE_EXCEPTION);