Re: Which of these selects is faster?

silveys_at_my-dejanews.com wrote:

> john0725_at_aol.com (John0725) 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.
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.
As for the ANDs, I think it's been there since V4, and I _know_ it's still there because of V6 backward compatibility.

I would need to check, but my best guess is the concepts manual is the place to find the documentation.

--
Met vriendelijke groet,
kind regards,

Frank van Bortel
Technical consultant Oracle
V&L Informatica BV

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