Thread

1. implementing outer joins

   Brett McCormick <brett@work.chicken.org> — 1998-07-03T02:35:40Z

   does anyone have any idea how difficult it would be to implement, and
   perhaps point me in the right direction?
   
   

2. Re: [HACKERS] implementing outer joins

   Bruce Momjian <maillist@candle.pha.pa.us> — 1998-07-03T04:08:14Z

   > 
   > does anyone have any idea how difficult it would be to implement, and
   > perhaps point me in the right direction?
   > 
   > 
   
   Good question.  My guess is that you have to set a flag in the
   RangeTblEntry for OUTER, and have this flag read by all the join
   methods.  Most(all?) of them have an inner and outer loop.  I think
   OUTER has to be in the outer part of the loop, and as you are spinning
   through the outer loop, if you don't find any matches in the inner loop,
   you output the outer loop with NULLs for the inner values.  Now if you
   have only two tables joined, and they are both outer, I am not sure how
   to handle that.
   
   Check out the new backend "How PostgreSQL Processes a Query" for hints
   on where to make changes.  (I have gotten no comments on the new
   version.)  Also check out the Developers FAQ for ideas too.
   
   
   -- 
   Bruce Momjian                          |  830 Blythe Avenue
   maillist@candle.pha.pa.us              |  Drexel Hill, Pennsylvania 19026
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3. RE: [HACKERS] implementing outer joins

   Stupor Genius <stuporg@erols.com> — 1998-07-03T14:49:51Z

   > 
   > does anyone have any idea how difficult it would be to implement, and
   > perhaps point me in the right direction?
   > 
   
   I forget where, but there is a place in the code where the two values
   of the join are compared to see whether the row qualifies.  Around
   this spot there is a check for one of the values being null and if it
   is, the function doesn't include the data.  Seems that modifying that
   spot or using it as a basis for your code could be a quick start for
   the left join.  The right could perhaps then be converted beforehand
   in the optimizer to a left to be handled there.
   
   But there's prolly a great and sane reason why this wouldn't work.
   
   Haven't thought about the full outer join yet.  Don't have my machine
   completely configured yet and it's hard to stay in to do that with it
   being summer and all.
   
   Later,
   darrenk