一段处理事务的代码

        $db->beginTransaction();
        $sql = "delete from user_base where uid=?";
        $st = $db->prepare($sql);
        $bRet = $st->execute(array($uid));
        if(!$bRet) {
            $db->rollBack();
            return false;
        }

        $sql = "delete from user_ext where uid=?";
        $st = $db->prepare($sql);
        $bRet = $st->execute(array($uid));
        if(!$bRet) {
            $db->rollBack();
            return false;
        }
        $db->commit();