For the SAME query, the costs can be compared - but
remember that the cost is basically just a
mathematical algorithm that pops out a number at the
end. It is somewhat analagous to the number of IO's
expected to satisfy the query, but of course
- Oracle can get it wrong occasionally
- its only as good as your optimizer stats
- By default, Oracle tends to undercost full table
scans (since it treats a single block IO the same as a
multiblock IO)
hth
connor
- Arn Klammer <Arn.Klammer_at_austrac.gov.au> wrote: >
Hi,
>
> Can you compare the costs that are displayed in
> explain plan output? For example, I have a query
> that contains a merge join. The cost reported in
> the explain plan is 134. By including a hint to use
> a nested loop instead, the cost becomes 1160. Does
> this mean the merge join plan is more efficient,
> despite generally being considered a less efficient
> join method than a NL?
>
> Thanx
>
> -a
>
>
>
>
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Received on Wed Dec 12 2001 - 04:13:52 CST
