Re: Which of these selects is faster?

2nd Try!!!

From

PL/SQL User's Guide and Reference
 Release 8.0
 A58236-01
Fundamentals

P2-47

Operator Precedence

The operations within an expression are done in a particular order depending on their precedence (priority). Table 2-2 shows the default order of operations from first to last (top to bottom).

I think this may be what you are looking for ??

Regards

Alex

Scott Silvey wrote:

> Frank van Bortel <f.van.bortel_at_vnl.nl> wrote:
> :>>If the where clause has ANDs then it is evaluated from the end of the query
> :>>towards the beginning, but if it has ORs it is evaluated starting closest to
> :>>the FROM clause and working its way downward.
> :>
> :> Thanks, it's helpful to know that things are sufficiently complex
> :> that it seems oracle did not intend for users to predict the order
> :> of evaluation. (That sucks of course, and I'd like to see them fix
> :> it so that you could at least have the option to force a certain
> :> order.)
> :>
> :> How did you come by this information? Trial and error? Oracle tech
> :> support? Actual documentation? Source code?
> :
> :It quite logical, and documented.
>
> Documented? WHERE?!
>
> :For the OR's, there's no point in evaluating, after a TRUE condition
> :is found (TRUE or FALSE still is TRUE)- so this way of evaluating will
> :actually speed up things.
>
> Obviously. Check the beginning of this thread and you'll see this is
> the whole point of the thread. The problem is, to exploit this
> optimization fully, you need to know ahead of time what the order
> of evaluation is. Furthermore, you need to know that this convention
> is deterministic and consistent across all versions.
>
> If Oracle has documented the order of evaluation, then they have a
> public contract with their developers and are obligated to guarantee
> that their engine behaves accoringly.
>
> THIS is what I seek. But few people seem to have a solid idea what
> goes on underneath and up to now nobody has said anything about
> documentation.
>
> :As for the ANDs, I think it's been there since V4, and I _know_
> :it's still there because of V6 backward compatibility.
>
> IT's still there? What do you mean by "IT"?
>
> :I would need to check, but my best guess is the concepts manual is
> :the place to find the documentation.
>
> I would probably have to use Oracle's online documentation. Can you
> provide an exact-word phrase from a subsection heading in the general
> document so I can do a search and perhaps find it?
>
> Thanks,
>
> Scott
Received on Fri Apr 16 1999 - 02:35:32 CDT