SQLite不保存主键[关闭]

The following code doesn't save a "eventid" in the sqlite db by default. I can see all the rows with echo but the event ID is emply... Any ideas why? Thanks a lot.

$now = time();
try{
if (!file_exists("testgb")){
    $db = new PDO('sqlite:testgb');
    $db->exec("CREATE TABLE guestbook (eventid INTEGER PRIVATE KEY,name VARCHAR(55), message TEXT, date DATETIME)");
}
$db = new PDO('sqlite:testgb');
$db->setAttribute(PDO::ATTR_ERRMODE, PDO::ERRMODE_EXCEPTION);
$db->exec("INSERT INTO guestbook (name, message, date) VALUES ('KIRILL', 'Hello!!', datetime($now, 'unixepoch'))"); 
$res = $db->query("SELECT * FROM guestbook");
foreach ($res as $row){
    echo $row['eventid']."<br>";
    echo $row['name']."<br>";
    echo $row['message']."<br>";
    echo $row['date']."<br>";
    echo "<hr>";
}
}catch (PDOException $e){
    echo $e->getMessage();
}

Would you like to add AUTOINCREMENT event id? and PRIMARY KEY?

$db->exec("CREATE TABLE guestbook (eventid INTEGER PRIMARY KEY AUTOINCREMENT,name VARCHAR(55), message TEXT, date DATETIME)");

EventID is not created as an AutoInc field. I'm not sure what the syntax is but if you look up CREATE TABLE for sqlite you'll find how to set it as a Auto Increment field.