I’m pretty sceptical about all the Oracle slogans – ‘The Information Company’ and so on.

Searching the Oracle database 11gR2 documentation for:

- antijoin ( http://www.oracle.com/pls/db112/search?remark=quick_search&word=antijoin )
returns 6 entries. Only one of these 6 entries provides a clue what antijoin is
http://download.oracle.com/docs/cd/E11882_01/server.112/e17118/statements_10002.htm#i2182875

- null aware
the first match : “Null aware antijoins” specified in “Table 1-5 Optimizer Features for Oracle Database 11g Releases”
on http://download.oracle.com/docs/cd/E11882_01/server.112/e17110/initparams164.htm#REFRN10141
and that’s the only meaningful search result.

Using the Oracle database 11gR2 documentation there is no way to know what’s all about when ‘Null aware antijoins’ are involved.
Organizations buy the software, pay support fees every year … have Metalink access.
Ouch, it hurts, there is nothing about ‘Null aware antijoin’ on Metalink too.

Just one bug with the following description:

Bug 9929660
”
Description
Incorrect Join information not invalidated properly in the case of null aware
antijoin queries.
”
And there is no way to understand this description since null aware antijoin is not documented( the customer who is trying to investigate for bugs that might affect his shop would just ignore this bug).

Why Oracle doesn’t document such new optimizer improvements in the documentation by providing
- examples in the first place(the way you did it) – I’m sure that the new feature was tested using examples, so examples are available for sure.
- the purpose of the improvment – ‘Null aware antijoins’ name of an improvement sounds great but when you don’t know the meaning, what’s the purpose to be mentioned.

It’s embarrassing that Oracle just mentions an improvement and that’s all. There is nothing else that will give some light what’s this improvement and how customers could benefit from it.

What’s you opinion? Why it is the way as it is now?
(as of now knowledge sharing of such improvements is not documented but posted on blogs, forums, oak table members’ books and so on.
It’s for sure that Oracle has the knowledge and it’s not so hard to publish it in the documentation )

I’m very thankful for your Oracle database related inputs and the the way it influences me.

Just curious, why it is not the way it seems right to me.

Thanks again.

If you are asking if there will be a null-aware version of the previous transformations that were not null-aware, the answer would be yes.

If the null-aware path is followed consistently, we should end up with virtually all transformations doubled with there null-aware twins, schoudn’t we?

[0041] Suppose T1.x has the following set of values: {NULL,5,8,11}. Query Q2, the transformed query generated by regular anti-join unnesting, incorrectly returns {NULL,5}.
[0042] Suppose the subquery in Q1 returns the following set of values {7,8,11} and T1.x has the same set of values {NULL,5,8,11}. The correct result of Q1 is {5}. Regular anti-join unnesting again incorrectly returns {NULL,5}.

Both of these cases demonstrate how the presence of NULL with a regular anti-join produce incorrect results.

I’m not sure if I understand your second question. If an anti-join is made null-aware, is it not a null-aware anti-join?

What do you think – why is the Null-Aware Anti-Join so special that it deserves a specially named query transformation? The “regular” Anti-Join can just be also null-aware, can’t it? Or is there any standard (patent) preventing that?

Your blog is a joy to read. Thank you for your contributions!

Thanks for the excellent article.

Regards,
Rob.