Malcolm Greene <> wrote:
> Are there any ways to optimize UNION performance - in general or with
> an Oracle 8.17 backend?
>
> I have 5 data sets that I need to merge via a UNION and the time to
> its to build each set individually is 9 secs but the time it takes to
> build the same set of data and union together into a single set is 33
> seconds.
>
> The total set size is 1M of records with the largest set being
> unioned being about 750K.
>
> I've tried rearranging the position of the big data set in the union
> process, but this does not affect performance.
>
> Any tips or am I just seeing what's pretty much standard overhead for
> performing unions.
Look at the JOINS needed for each query.
Stephen Russell
DBA / .Net Developer
Memphis TN 38115
901.246-0159
"A good way to judge people is by observing how they treat those who
can do them absolutely no good." ---Unknown
http://spaces.msn.com/members/srussell/
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