well superman is poorer than batman
-----Original Message-----
Sent: 22 September 2003 13:45
To: Multiple recipients of list ORACLE-L
Yeah, Superman had Super powers. Batman just relied on a bunch of gadgets.
Of course my original post was implying the classic "it depends". There
are some scenario's where a specific approach is faster than the other and
there are some scenario's where it doesn't matter because oracle can
rewrite the query effectively anyway. What does matter - "If in doubt test
it out".
"Sinardy Xing"
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Sent by: Subject: RE: minus vs. where not
exists, vs. where not in
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22/09/2003 15:29
Please respond to
ORACLE-L
I think Superman is stroger than Batman
-----Original Message-----
Sent: 22 September 2003 08:30
To: Multiple recipients of list ORACLE-L
I'm not sure that there is a good answer to that question. The question
sounds like the dilemma: who's stronger, Batman or Superman?
Unfortunately, superheroes do not exist, so we cannot have a real life
comparison. It is exactly the same with not exists vs. minus. Comparisons
make
sense only within a real life application in a real configuration, that is
why both mechanisms are provided. Sort_area_size does influence
performance,
unless memory is slow, system is swapping or something else.
In the world of superheroes, my favorite is Alice and her "fist of death".
On 2003.09.21 19:54, Mark Richard wrote:
>
> I don't have any scientific proof but I imagine the sort_area_size could
be
> different between "not exists" and "minus". When doing "minus" the
entire
> select string would have to be compared for equality, which could be very
> large depending on your string.
>
> Minus is probably an easier way (at least from a coding perspective) of
> comparing every column in a table, or incorporating complexity in the
> select statement.
>
> Having said that. Each statement has it's pros and cons and I guess it
> depends on the volume of the various queries, etc. For example, if the
> have table A with 5 rows and table B with 1000000 rows executing "select
> a.field from a where not exists (select 1 from b where b.field = a.field)
> will result in 5 quick searches (assuming b.field is indexed) whereas
> "select a.field from a where a.field not in (select b.field from b)" will
> result in a full index read of b, as would "select a.field from a minus
> select b.field from b". Obviously different queries and different
volumes
> will tip the scales in different directions.
>
> Regards,
> Mark.
>
>
>
>
>
> "Ryan"
>
> <[EMAIL PROTECTED] To: Multiple
recipients
> of list ORACLE-L <[EMAIL PROTECTED]>
> > cc:
>
> Sent by: Subject: minus vs. where
not
> exists, vs. where not in
> [EMAIL PROTECTED]
>
> .com
>
>
>
>
>
> 22/09/2003 03:59
>
> Please respond to
>
> ORACLE-L
>
>
>
>
>
>
>
>
>
> Do any of you have any cases when minus is superior in performance? Ive
> found 'not in' with a hash_aj to be the best option if the sub-query is
> significantly less 'costly' then the outer query. I dont mean cost in
terms
> of the Explain Plan, I mean the work Oracle has to do to find a result
set.
> It also depends on a proper hash_area_size
>
> I find 'where not exists' to be best if the subquery is relatively close
in
> cost to the outer query. Yes I know you cant make broad generalizations,
> but there has to be some 'narrow' generalizations you can make. Such as
> certain cases, etc...
>
> what have you seen? There seems to be very little work in this area in
the
> literature.
>
> Does 'where not exist' need more or less sort_area_size space than minus?
>
>
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