Re: O9i: general index question

Thorsten Kettner schrieb am 03.04.2007 in <1175611301.279065.237280_at_n76g2000hsh.googlegroups.com>:

> On 3 Apr., 16:05, Andreas Mosmann <mosm..._at_expires-30-04-2007.news-
> group.org> wrote:

>>>> I want to stay with '0000000000' because Oracle does not store NULL into
>>>> a column and so I had bad results using ... IS NULL
>> 
>> Sorry: replace('column','index')

> Oracle doesn't store NULL entries in indexes, true. But this is only
> to save memory and to gain speed and shouldn't make any difference to
> your select result at all. Maybe you mean bad performance, not bad
> results?

yes, of course. It is because of the kind of Denglish I speak. result is misunderstandable, sorry.

>> btw: Can you tell me how to specify a driving table?

> You cannot really. Oracle uses an optimizer which analyzes your query
> and tries to make the best of it. In my experience this works very
> good for more then 99% of all queries. So there is not much you can
> do. Normally it works automatically, because from your where clause
> the optimizer can evaluate which tables to access first. You can
> however use a hint: select /*+RULE*/ ... would switch off the
> optimizer and would use the tables in the order as your selects states
> them (I think it was last one first, but I am not sure). Usually
> however this results in a slower execution, but you can use it for
> testing anyhow. A compromise is select /*+ORDERED*/ ... which uses the
> optimizer, but tells it to have a look at your table order. (With
> hints you can also force usage of a particular index. Advice however
> is not to use them. We use them when it is obvious that the optimizer
> fails on a query, which is extremely rare.)
I will try it.

> My advice: Try it with NULL instead of '0000000000' once more. This is
> what we all use, so it should work for you too.
If you are that convinced a second try has to be done :)

Thank you
Andreas Mosmann

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