为什么在我的代码PDO中lastInsertId（）返回0？

Question

I am trying to get the last record from the database using lastInsertId() but it keeps retuning 0. I don't understand why this problem occurs. Here is my code. Thanks

$query = "SELECT url FROM links WHERE code = :code";
$get = $db->prepare($query);
$get->execute(array(
    ":code" => $code
));

if($get->rowCount()) {
    $url = $get->fetch(PDO::FETCH_OBJ)->url;

    $status = substr(get_headers($url)[0],9,3);

    if(intval($status) == 301) {
        $last = $db->lastInsertId();

        $query = "SELECT url FROM links WHERE id = :id";
        $send = $db->prepare($query);
        $send->execute(
            ":id" => $last
        );

        $lastUrl = $send->fetch(PDO::FETCH_OBJ)->url;
        header("Location:{$lastUrl}");
    }
    else {
        header("Location:{$url}");
    }

    die();
}

Answer 1

There's no INSERT in the code.

I guess you're looking for the biggest id in the table. Then the answer would be:

SELECT MAX(id) FROM links

Answer 2

lastInsertId() works on the last query. Your query is SELECT type that is why it won't work. You can use lastInsertId() after INSERT query. If you wan to know last record you can use max(id) or sort it by id desc and get first one.

http://php.net/manual/en/pdo.lastinsertid.php