move omit/unexpose fields operation to query phase

e.g:

``` js
SELECT r.id, r.name, r.age
FROM root r
WHERE r.name="val" AND r.age="val"
```

The issue mentions moving an 'omit/unexpose fields operation' to the query phase, referencing a SQL-like query. Look for query processing code in the repository, likely in files handling SELECT or WHERE clauses. Understand how fields are currently omitted or exposed, then refactor to integrate this logic earlier in the query pipeline. Check for existing tests related to query execution to ensure changes don't break functionality.

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