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From lockhart@alumni.caltech.edu Thu Jan 7 13:31:08 1999
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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 don't yet pass an explicit join node into the planner/optimizer, and
that will be the hardest part I assume. Perhaps we can work on that
together.
So, what I'll try to do (soon, in the next few days?) is put in
#ifdef ENABLE_OUTER_JOINS
conditional code into the parser area (already there for the executor)
and commit everything to the development tree. Does that sound OK?
Oh, and if anyone is looking for something to do, I've got a couple of
CASE statements in the case.sql regression test which are commented out
because they crash the backend. They involve references to multiple
tables within a single result column, and in other contexts that
construct works. It would be great if someone had time to track it
down...
- Tom
From lockhart@alumni.caltech.edu Mon Feb 22 02:01:13 1999
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> How do you propose doing outer joins in non-mergejoin situations?
> Mergejoins can only be used currently in equal joins.
Is your solution going to be to make sure the OUTER table is always a
MergeJoin, or on the outside of a join loop? That could work.
That could get tricky if the table is joined to _two_ other tables.
With the cleaned-up optimizer, we can disable non-merge joins in certain
circumstances, and prevent OUTER tables from being inner in the others.
Is that the plan?
--
Bruce Momjian | http://www.op.net/~candle
maillist@candle.pha.pa.us | (610) 853-3000
+ If your life is a hard drive, | 830 Blythe Avenue
+ Christ can be your backup. | Drexel Hill, Pennsylvania 19026
From lockhart@alumni.caltech.edu Mon Mar 1 13:01:08 1999
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> How do you propose doing outer joins in non-mergejoin situations?
> Mergejoins can only be used currently in equal joins.
Hadn't thought about it, other than figuring that implementing the
equi-join first was a good start. There is a class of outer join syntax
(the USING clause) which is implicitly an equi-join...
- Tom
From lockhart@alumni.caltech.edu Mon Mar 8 21:55:02 1999
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