何为PDO？

<?php
$db = new PDO(‘mysql:host=localhost;dbname=test‘, $user, $pass);
//使用新建立的数据库连接。
//... ...
//连接在PDO实例的生命周期里是活动的。使用完毕后应当关闭此连接，若不这样做PHP在代码结束时才关闭此连接，将占用一部分内存。
$db = null;
?>

<?php
$db = new PDO(‘mysql:host=localhost;dbname=test‘, $user, $pass, array(
    PDO::ATTR_PERSISTENT => true
));
?>

$sth = $db->prepare(‘select * from book where cat_id=:id limit :offset, :limit‘, array (
PDO :: ATTR_CURSOR => PDO :: CURSOR_FWDONLY
));
//用$limit1得到一个结果
$result1 = $sth->execute(array (
        ‘:id‘ => $cat,
        ‘:offset‘ => ($pg -1) * $limit1,
        ‘:limit‘ => $limit1
    ));

//用$limit2得到另一个结果
$result2 = $sth->execute(array (
        ‘:id‘ => $cat,
        ‘:offset‘ => ($pg -1) * $limit2,
        ‘:limit‘ => $limit2
    ));

//用位置参入参数
$stmt = $dbh->prepare("INSERT INTO REGISTRY (name, value) VALUES (?, ?)");
$stmt->bindParam(1, $name);
$stmt->bindParam(2, $value);

//用名称传入参数
$stmt = $dbh->prepare("INSERT INTO REGISTRY (name, value) VALUES (:name, :value)");
$stmt->bindParam(‘:name‘, $name);
$stmt->bindParam(‘:value‘, $value);

$name = ‘one‘;
$value = 1;
$stmt->execute();

/////////////////////////////////////////////
//也可以这样实现
//用位置参入参数，indexed array
$stmt = $dbh->prepare("INSERT INTO REGISTRY (name, value) VALUES (?, ?)");
$name = ‘one‘;
$value = 1;
$stmt->execute(array($name,$value));

//用名称传入参数, associated array
$stmt = $dbh->prepare("INSERT INTO REGISTRY (name, value) VALUES (:name, :value)");
$name = ‘one‘;
$value = 1;
$stmt->execute(array(‘:name‘=>$name,‘:value‘=>$value));

// placeholder must be used in the place of the whole value
$stmt = $dbh->prepare("SELECT * FROM REGISTRY where name LIKE ?");
$stmt->execute(array("%$_GET[name]%"));

//下面这样就有问题了
$stmt = $dbh->prepare("SELECT * FROM REGISTRY where name LIKE ‘%?%‘");
$stmt->execute(array($_GET[‘name‘]));