On 17.07-17:31, Mary Anderson wrote:
[ ... ]
> I am most worried about the second select, with its 'NOT EXISTS'
> statement slowing everything down. I would put appropriate indexes on
> this -- namely an index on series for data and an index on dhd for
> da_id. My user community is a bunch of academics, so I am not under
> the performance constraints I would have for a business application.
> Would it help performance if I denormalized the database by attaching
> series to the data_has_dimensions table?
to be honest i couldn't really understand your SQL but that probably
says more about me than you. either way i don't think you need to
worry about the NOT EXISTS statement. generally, serialising select
statements is better than joining and would suggest that if your series
data has 10,000 rows (assuming 10,00 was a typo) then i wouldn't merge
that data with another table (it also will simply mean a larger,
disjoint table, essentially equivelant to the join table required your
queries and thus may well cost you in overall performance). i would
suggest you try to restructure you queries to serialise the 'series'
select joins (and preferably only doing it once), thereby reducing
the final join table to a minimum.
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