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From Maryann Xue <maryann...@apache.org>
Subject Re: Why hint does not traverse down subquery alias
Date Wed, 12 Jun 2019 01:14:57 GMT
BTW, I've actually just done some work on hint error handling, which might
be helpful to what you mentioned:

https://github.com/apache/spark/pull/24653

On Tue, Jun 11, 2019 at 8:04 PM Maryann Xue <maryann.xue@databricks.com>
wrote:

> I believe in the SQL standard, the original name cannot be accessed once
> it’s aliased.
>
> On Tue, Jun 11, 2019 at 7:54 PM John Zhuge <jzhuge@apache.org> wrote:
>
>> Yeah, it is a touch scenario.
>>
>> I actually have much simpler cases:
>>
>> 1) select /*+ broadcast(t1) */ * from db.t1 join db.t2 on t1.id = t2.id;
>> 2) select /*+ broadcast(t1) */ * from db.t1 a1 join db.t2 a2 on a1.id =
>> a2.id;
>>
>> 2) is the same as 1) but with aliases. Many users were surprised that 2)
>> stopped working.
>>
>> Thanks,
>> John
>>
>>
>> On Tue, Jun 11, 2019 at 4:38 PM Maryann Xue <maryannxue@apache.org>
>> wrote:
>>
>>> Yes, and for a good reason: the hint relation has exactly the same scope
>>> with other elements of queries/sub-queries.
>>>
>>> Suppose there's a query like:
>>>
>>> select /*+ broadcast(s) */ from (select a, b from s) t join (select a, b
>>> from t) s on t1.a = t2.b
>>>
>>> If we allowed the hint resolving to "cross" the scopes, we'd end up with
>>> a really confusing spec.
>>>
>>>
>>> Thanks,
>>> Maryann
>>>
>>> On Tue, Jun 11, 2019 at 5:26 PM John Zhuge <jzhuge@apache.org> wrote:
>>>
>>>> Hi Reynold and Maryann,
>>>>
>>>> ResolveHints javadoc indicates the traversal does not go past subquery
>>>> alias. Is there any specific reason?
>>>>
>>>> Thanks,
>>>> John Zhuge
>>>>
>>>
>>
>> --
>> John Zhuge
>>
>

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