inner or outer join?

[Khailenka Xenia <xe...@tut.by>]

There is a question which join strategy would be better to use implicitly
when supporting the relationship with the other entity - inner or outer. On
the one hand, the inner join allow to avoid entities with null references
when we want to restrict the result set, on the other hand we can lose these
entities when we not care about those references. Now the outer join is
implicitly used and that results in ability to get the null entity at the
result set. Any thoughts?

-- 
Regards, Ksenia Khailenko

Re: inner or outer join?

[Andrus Adamchik <an...@objectstyle.org>]

On Jan 26, 2010, at 1:19 PM, Andrey Razumovsky wrote:

> I'm very surprised it is left join by default. I think it should be  
> inner
> join, as it is also analogue with SelectQuery (e.g. "artist" path in
> expression means inner Join).

I am somewhat 50/50, or maybe 60/40 in favor of inner. SelectQuery has  
no exact precedent as it doesn't allow for paths in SELECT clause. Of  
course implicit path's in all other places (such as WHERE) result in  
INNER joins. Except for a special case of flattened attributes/ 
relationships, that started using OUTER joins since 3.1 (the idea  
being that NULL flattened attributes should be allowed).

So here the decision is whether the case we are talking about is more  
like a general rule ("a path anywhere in the query results in an inner  
join, unless it is explicitly specified as OUTER"), or more like a  
flattened rule.

Since I hope in 3.1 we'll allow path+ outer join syntax anywhere in  
the query, I guess the default should be inner.

> What does specification say?

Nothing useful that I could find except for implicit hint at INNER  
when explaining how COUNT(p.artist) should work (but I didn't search  
extensively). Now I also can't remember why we decided to use OUTER  
JOIN in the first place :-)

Andrus

Re: inner or outer join?

[Andrey Razumovsky <ra...@gmail.com>]

I'm very surprised it is left join by default. I think it should be inner
join, as it is also analogue with SelectQuery (e.g. "artist" path in
expression means inner Join). What does specification say?

2010/1/26 Andrus Adamchik <an...@objectstyle.org>

> We had an offline conversation about that with Ksenia. I should clarify
> that we are talking about EJBQL "SELECT" clause. As in  "SELECT p.artist
> FROM Painting p"
>
> Andrus
>
>
> On Jan 26, 2010, at 12:35 PM, Khailenka Xenia wrote:
>
>  There is a question which join strategy would be better to use implicitly
>> when supporting the relationship with the other entity - inner or outer.
>> On
>> the one hand, the inner join allow to avoid entities with null references
>> when we want to restrict the result set, on the other hand we can lose
>> these
>> entities when we not care about those references. Now the outer join is
>> implicitly used and that results in ability to get the null entity at the
>> result set. Any thoughts?
>>
>> --
>> Regards, Ksenia Khailenko
>>
>
>


-- 
Andrey

Re: inner or outer join?

[Andrus Adamchik <an...@objectstyle.org>]

We had an offline conversation about that with Ksenia. I should  
clarify that we are talking about EJBQL "SELECT" clause. As in   
"SELECT p.artist FROM Painting p"

Andrus

On Jan 26, 2010, at 12:35 PM, Khailenka Xenia wrote:

> There is a question which join strategy would be better to use  
> implicitly
> when supporting the relationship with the other entity - inner or  
> outer. On
> the one hand, the inner join allow to avoid entities with null  
> references
> when we want to restrict the result set, on the other hand we can  
> lose these
> entities when we not care about those references. Now the outer join  
> is
> implicitly used and that results in ability to get the null entity  
> at the
> result set. Any thoughts?
>
> -- 
> Regards, Ksenia Khailenko