AppleII717 wrote in post #959561:
> I could do:
> income = Item.joins(:account).where('account.type' => "Income")
>
> Or, I could do:
>
> income = Item.where(:account_id => Account.where(:type =>
> "Income").map(&:id))
>
> While there are several others queries where this is used, the joins
> approach takes about 20ms in activerecord. The in approach (the inner
> query produces an array of ids) takes about 10ms.
>
> Numbers tell me that my array approach is better, but then I have not
> seen many use that approach.
I don't know how extensive (i.e. how many scenarios) your benchmarking
involved, but if it was only one contrived test that may not be enough.
For example what effect does an increasing number of values in the in()
have on performance?
Searching a single table on an indexed simple integer is obviously going
to be faster than a join. However, as the number of values in the "in"
clause increases you need to know how that affects performance. For
example in(1,2) might be significantly different than
in(1,3,5,7,20,50,100,200).
My point is that performance of an in() likely doesn't increase linearly
with the number of values.
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