It depends on what you're doing. The use of a join
technique over another depend on how much data you
need to access.
If you read very few information from both tables then
a nested loop is the fastest way to get data. To use a
nested join at a cheap cost you need a good index on
the outer table.
On the other hand, if your query output contained
allmost all data from both tables than an hash join or
a sort merge is better than a nested loop.
If you're in a DW and have data organized with
dimension and fact tables than the optimiser should be
using star transformation.
- "Leonard, George" <george.leonard_at_farnell.com> a
écrit : > Hi there
>
> Can someone please give me in order of
> preference/cost the relevant costs
> for the different joins.
>
> IE:
>
> This join is cheap,
> This is very expensive,
> This is bad and always avoid.
>
>
> George
> ________________________________________________
> George Leonard
> Oracle Database Administrator
> Dimension Data (Pty) Ltd
> (Reg. No. 1987/006597/07)
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> E-mail:george.leonard_at_za.didata.com
> Web: http://www.didata.co.za
>
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Received on Mon Oct 07 2002 - 15:33:23 CDT
