Github user davies commented on the pull request:
https://github.com/apache/spark/pull/10678#issuecomment-172947664
@gatorsmile I took a pass, it's correct overall. My only concern is that
it's too powerful that could introduce some side effects that we don't want.
For example:
```
df.select('a).limit(10).orderBy('b)
```
We may not want support these complicated use case. With DataFrame API, we
could easily construct a plan as we want.
Without subquery, SQL query can only have one SELECT clause, it's
reasonable to support that (at least other database support that), or you have
to use subquery.
Here is the cases that we should support:
```
SELECT project_list FROM tables GROUP BY keys HAVING condition ORDER BY
ordering LIMIT N
```
The columns used in HAVING and ORDER BY could be not presented in SELECT,
we should still resolve them.
Between Sort and Join/Scan, it could have Project/Filter/Window/Aggregate,
no others.
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