$this->PDOStatement = null;
        if ($clear_cache) {
            /* @var $dbCache DBCache */
            $dbCache = Ioc::get(DBCache::class);
            $dbCache->deleteCache($sql);
        }
        try {
            // 调试开始
            // 预处理
            $this->PDOStatement = $pdo->prepare($sql);
            // 参数绑定
            $this->bindValue($bind);
            // 执行查询

            $this->PDOStatement->execute();
        } catch (\PDOException $e) {
            $error = $e->errorInfo;
            //2006和2013表示表示连接失败,需要重连接
            if ($error[ 1 ] == 2006 || $error[ 1 ] == 2013) {
                $this->pdo = null;
                $this->connect();
                $this->execute($sql, $bind);
            } else {
                throw $e;
            }
        }
    }

    /**
     * 切换数据库
     *
     * @param string $db
     */
    public function userDb($db) {
        $pdo = $this->connect();
        // 根据参数绑定组装最终的SQL语句
        try {
            $pdo->exec("use " . $db);
        } catch (\PDOException $e) {
            $error = $e->errorInfo;

    
PDO->prepare(...)
rap\db\Connection->execute(...)
rap\db\Connection->query(...)
rap\db\Select->findAll(...)
rap\db\Select->find(...)
rap\db\Record::find(...)
cloud\SiteConfig->handler(...)
rap\web\Application->start(...)
require(...)