All columns are selected by default?

When I print out the raw sql command, I found that all columns are selected. Does it make sense?

I think only those specified from the frontend should be included. The following command is how I get the raw sql.

`print(query.statement.compile(compile_kwargs={"literal_binds": True}))`

Thanks.

從建構 GraphQL-to-SQLAlchemy 查詢開始，該查詢會產生由 query.statement.compile(compile_kwargs={"literal_binds": True}) 顯示的陳述式。追蹤前端選取的欄位如何表示，並確認是否可以排除未要求的欄位。完成條件是產生的 SQL 只選取要求的欄位，並有一個回歸測試涵蓋該行為。

由索引模型根據 Issue 內容生成。