mysql更新php后的空值

i made a lot of research around here and Google but i cannot find an answer to this problem.

I update a field in a MySQL database with following code:

public function registerPubKey() {

    $stmt = $this->cn->prepare('UPDATE sb_user SET pubkey= ? WHERE email= ?');
    $exres = $stmt->execute(array($this->info["pubkey"],$this->info["email"]));
    if ($exres == false) { $resultArray["result"] = "Error registering public key"; echo json_encode($resultArray); exit; }

    $resultArray["result"] = "success"; echo json_encode($resultArray);
}

I'm sure that all works except that the field in the database is empty. I dumped the private variable $info and it contains the pubkey (pubkey is a base64 string).

I noticed that if I change the update query with an INSERT, the value is inserted correctly!

It's likely because you're trying to UPDATE non existent rows. Try adding a ON DUPLICATE KEY before. See INSERT ... ON DUPLICATE KEY UPDATE Syntax. UPDATE returns nothing if the row does not exist.