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From Andrus Adamchik <and...@objectstyle.org>
Subject Re: inner or outer join?
Date Tue, 26 Jan 2010 11:32:15 GMT

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

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