PHP用Where子句读取XML

Let's say I have this XML file.

<book>
    <id>1</id>
    <title>Harry Potter - bla bla bla</title>
    <author>J.K Rowling</author>
</book>
<book>
    <id>2</id>
    <title>Other book</title>
    <author>A Name</author>
</book>

Is there a way where I can read via PHP and get the #2 id, or do I have to use an IF? Like jQuery selector ':eq(2)', or MySql 'WHERE id=2'

If all you want is just the second one you can use DOM. It's simpler.

$dom->loadXML(<<<XML
<book>
    <id>1</id>
    <title>Harry Potter - bla bla bla</title>
    <author>J.K Rowling</author>
</book>
<book>
    <id>2</id>
    <title>Other book</title>
    <author>A Name</author>
</book>
XML;);

$book=$dom->getElementsByTagName('book')->item(1);

Edit: I just saw you say you were looking for second ID, not second element, you need xpath for that.

$xml=new SimpleXMLElement(<<<XML
<book>
    <id>1</id>
    <title>Harry Potter - bla bla bla</title>
    <author>J.K Rowling</author>
</book>
<book>
    <id>2</id>
    <title>Other book</title>
    <author>A Name</author>
</book>
XML;);
$result=$xml->xpath('/book[id=2]');