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Home -> Community -> Mailing Lists -> Oracle-L -> Re: What I'm doing? explanation about my posts
Juan,
Your goal of providing informative articles is laudable.
You might want to consider the following 2 queries more closely.
SQL> select count(*) from daz.utl_tablas_me
2 where tbl_dsm in
3 (select null from daz.utl_tablas_me);
COUNT(*)
0
This query proves that an arbitrary column is never equal to null.
SQL> select count(*) from daz.utl_tablas_me 2 where exists(select null from daz.utl_tablas_me); COUNT(*)
310
This query also proves that an arbitrary column is never equal to null, and in addition, proves that there are 310 rows in the utl_tablas_me table.
It doesn't tell you anything about the value of any column in the utl_tablas_me table, including whether or not any of the columns are null.
>From the examples it is unclear what you are trying to prove.
Maybe you just need different examples?
Jared
"Juan Cachito Reyes Pacheco" <jreyes_at_dazasoftware.com>
Sent by: oracle-l-bounce_at_freelists.org
02/20/2004 11:43 AM
Please respond to oracle-l
To: <oracle-l_at_freelists.org>
cc:
Subject: What I'm doing? explanation about my posts
Hi,
I like to write articles, at the same time I investigate something I share
it to other so it could be useful, I did one Tom Kyte check (about
flashback) but he didn't have more time.
I ask Burleston if he would have time, because I saw he likes some
communitary activities, but he neither ansewr my email.
What I'm doing now is posting interesting topics, principally brief, for
every one, I am including in an article about basic tuning (bulk
collection,
null in in() ) I soonly will put in my page on geocities, so based on the
feedback to improve,
The idea is a very simple explanation and introduction, but enough clear,
so
if you want more information you go to tahiti.oracle.com, search and get a
copmlete answer.
for example I improved in() explanation
When comparing any value using IN with NULL values, IN don't return TRUE
hence, ignore null values as you can see in the table there are 310 null
values in column TBL_DSM.
SQL> select count(*) from daz.utl_tablas_me
2 where tbl_dsm in
3 (select null from daz.utl_tablas_me);
COUNT(*)
0
SQL> select count(*) from daz.utl_tablas_me
2 where exists(select null from daz.utl_tablas_me);
COUNT(*)
310
A more clear example of this situation you can see in this way
select count(*) from dual where null in (null );
COUNT(*)
0
bulkcollection to ...
During execution, every SQL statement causes a context switch between the two engines. Performance can be improved reducing the number of contexts switches using FORALL for bulk collection to one.
If you don't like you can simply ignore this posts :) Happy Carnaval
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