Re: performance advice needed: join vs explicit subselect

Karsten Hilbert wrote:
> Hello all,
>
> maybe some general advice can be had on this:
>
> table test_results
> modified_by integer foreign key staff(pk),
> intended_reviewer integer foreign key staff(pk),
> actual_reviewer integer foreign key staff(pk)
>
> (this table will contain millions of rows)
>
> table staff
> pk integer
> name text
>
> (this table will contain at most 50 rows)
>
> Now I want to set up a view which aggregates test results
> with staff names for all three foreign keys. This would mean
> I would either have to
>
> - join test_results to staff three times, once for each
> of the foreign keys, this is going to be messy with
> tracking table aliases, duplicate column names etc
>
> - write three explicit sub-selects for the columns I want
> to denormalize into the view definition
>
>
Select testresults.*, Modifer.Name, Intended.name, Actual.name from
testresults
left join (Select pk, name from staff) Modifer
on Modifer.pk = testresults.modified_by
left join (Select pk, name from staff) Intended
on Reviewer.pk = testresults.intended_reviewer
left join (Select pk, name from staff) Actual
on pk = testresults.actual_reviewer

This is what i think you are after. You can do this via nested queries
also for each name