RE: [HACKERS] Outer Joins (and need CASE help)

> > Thomas, do you need help on outer joins?
> 
> Yes. I'm going slowly partly because I get distracted with other
> Postgres stuff like docs, and partly because I don't understand all of
> the pieces I'm working with.
> 
> I've identified the place in the MergeJoin code where the null filling
> for outer joins needs to happen, and have the "merge walk" code done.
> But I don't have the supporting code which actually would know how to
> null-fill a result tuple from the left or right. I thought 
> you might be
> interested in that?
> 
> I've done some work in the parser, and can now do things like:
> 
> postgres=> select * from t1 join t2 using (i);
> NOTICE:  JOIN not yet implemented
> i|j|i|k
> -+-+-+-
> 1|2|1|3
> (1 row)
> 
> But this is just an inner join, and the result isn't quite right since
> the second "i" column should probably be omitted. At the moment I
> transform it from the syntax above into existing parse nodes, and
> everything from there on works.

I could be wrong (I don't have a copy of the standard), but I don't
believe that the above syntax follows the standard.  Let me know if I'm
wrong, but my understanding of the syntax would be more like:SELECT * FROM t1 JOIN t2 ON (t1.i = t2.i);
with the same result set as you listed (t2.i isn't suppressed).
This would have a difference in approach from the above.  If I wanted to
join on columns with different names I couldn't use your syntax (as one
example).-DEJ