RE: SOLVED?: Oracle interprets ANSI Inner Join as an Outer Join?
- From: "Mark W. Farnham" <mwf@xxxxxxxx>
- To: <rgravens@xxxxxxxxx>, <jkstill@xxxxxxxxx>
- Date: Fri, 25 Sep 2009 05:28:20 -0400
Without arguing with your conclusion, I have a few problems with your
example and one of your points.
First, I'm guessing you really meant the outer join to be on a.col1 =
b.col1. Otherwise you're filtering tabb to eliminate rows where col1 is null
and there is no equijoin at all.
Second, there is a really easy to distinguish the meanings in "traditional"
(+) syntax. In fact writing that clearly establishes filters on the row
sources in the from clause is arguably clearer. (But I am not making that
argument here.)
select *
from
taba a,
(select * from tabb where col2 is null) b
where a.col1 = b.col1(+);
is crystal clear, at least to me. Likewise
select *
from
taba a,
tabb b
where a.col1 = b.col1(+)
and b.col2 is null
is clear that only tuples where b.col2 is null are allowed in the result
set, whether the tuple portion existed in tabb or was created in service of
the outer join to taba.
Finally, if you made the equivalent typo that I *presumed* you made in my
*guess* (sorry Alex - but I'd need to do an extra ack-nak with Rumpi and
wait for his reply to avoid a guess)
then Oracle would helpfully respond:
ORA-01416: two tables cannot be outer joined together
(although in this case I suppose "a table cannot be outer joined to itself"
might be a better message)a
and that would force you to write something like
select *
from
taba a,
(
select * from tabb
where col1 is not null
and col2 is null
) b
if that is what you meant.
I haven't read your paper (yet), and I'll be the first to excuse typos in
quick helpful list responses (how many times have I typed the reverse of
what I meant UNDO/REDO? [many
and that's a rhetorical question]). So please do not anyone think this is
any sort of flame nor a quasi religious defense of (+) syntax, as I intend
no argument. And I look forward to reading your paper.
Regards,
mwf
_____
From: oracle-l-bounce@xxxxxxxxxxxxx [mailto:oracle-l-bounce@xxxxxxxxxxxxx]
On Behalf Of Rumpi Gravenstein
Sent: Wednesday, September 23, 2009 11:07 PM
To: jkstill@xxxxxxxxx
Cc: sacrophyte@xxxxxxxxx; ORACLE-L
Subject: Re: SOLVED?: Oracle interprets ANSI Inner Join as an Outer Join?
<snip>It is simpler to write, and easier to read IMO.</snip>
I agree!
This is a topic close to my heart. In my view one should only use the ANSI
syntax. The Oracle SQL documentation recommends it for outer joins. I
recommend it for all joins.
Here are some of the reasons:
ANSI outer joins have more power as they distinguish between these two
statements which can't easily be distinguished with the traditional syntax:
SELECT *
FROM taba A
LEFT OUTER JOIN tabb B
ON ( b.col1 = b.col1
AND b.col2 IS NULL
)
and
SELECT *
FROM taba A
LEFT OUTER JOIN tabb B
ON ( b.col1 = b.col1
)
WHERE b.col2 IS NULL
The first applies the b.col2 IS NULL filter before the outer join is
attempted while the second applies the filter after the outer join is
completed. That can lead to completely different results!
Also, writing "correct" ANSI FULL join syntax is easy while doing the same
with the traditional (+) syntax is not.
I love the CROSS JOIN statement as it explicitly states what you want
instead of leaving it to comments/reader who may later think the SQL
statement is in error.
As for the INNER syntax, the close juxtaposition of the table and the join
condition makes the statement eminently more readable and therefore easier
to maintain.
One caveat. Stay away from the NATURAL join as it can lead to trouble. My
recommendation is to always use the ON syntax to specify table join
conditions.
I could go on and on on this topic but wont as I've done it in a
presentation last year...
Rumpi Gravenstein
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