Re: Suggestions for first exam ...

Oracle's implemention of the UNION does not involve a hash table. The data from the two sources involved in the UNION are sorted so that duplicates are removed.

HTH,
Brian

ctcgag_at_hotmail.com wrote:
>
> Brian Peasland <dba_at_remove_spam.peasland.com> wrote:
> >
> > From the Oracle education materials, if I remember them correctly, the
> > advice on avoiding sorts whenever possible was not meant that you should
> > not do a sort if you need to return data in a specific order. That is
> > impossible. Rather, it was meant to make you think on whether you needed
> > the sort at all. For instance, do you really need to use UNION (which
> > needs a sort) when UNION ALL will do (which doesn't need a sort). That
> > sort of thing was what the materials were referring to.
>
> Apropos of little, a UNION can theoretically be performed without
> sorting by using a hash table. Does Oracle entertain this possibility?
>
> I imagine it would brutalize many poor saps who don't specify "order by"
> but assume it will be sorted anyway.
>
> Xho
>
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Brian Peasland
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