Enable SQL features selectively

Hello,
given the breadth of the parser, it would be nice if it would be possible to selectively enable features on an opt-in basis.

Let's imagine an application where only a subset of SQL is supported. In this case, the application would need to check for every possible unsupported feature manually (e.g. if I don't support windowing in queries, I would need to check if the `named_window` field in the `Select` gets populated and abort).

It would be interesting, instead, to decide beforehand which feature set is to be supported, so that only "valid" SQL gets parsed and arrives to the application.

Thanks.

此 issue 未指出檔案、測試或進入點。先找出 parser 的 feature 處理進入點與現有的 parser 測試，接著定義如何選取受支援的 feature 集合，以及如何在不支援的 SQL 到達應用程式之前拒絕它。

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