我有以下代碼:檢查時PDO取select語句返回null
$check = $dbh->prepare("SELECT * FROM BetaTesterList WHERE EMAIL = ?");
$check->execute(array($email));
$res = $check->fetchAll();
if (!($res['EMAIL'])){
$stmt = $dbh->prepare("INSERT INTO BetaTesterList(EMAIL) VALUES (?)");
$stmt->execute(array($email));
} else {
$return['message'] = 'exists';
}
然而,這仍然插入值雖然記錄在數據庫中已經存在。我如何防止這種情況?