Hi Gabriel,

In your first query, the values bound to the variable in the second
for clause will be limited to the first 100 results. This is the
reason why this path expression cannot be rewritten for index access.
Things look different in the second query, in which the second for
clause can be rewritten (because there is no positional limitation).

Hope this helps,
Christian

> for $cat in doc('expdb/auction.xml')/site/categories/category[position() >=
> 1 and position() < 101]
> for $pe in doc('expdb/auction.xml')/site/people/person
> where count($pe/profile/interest) > 3 and $pe/profile/interest/@category =
> $cat/@id
> return
>     <match>
>         <person>{$pe/name}</person>
>         <category>{$cat/name}</category>
>     </match>
>
> the optimized query changes to:
>
> for $cat_0 in
> db:open-pre("expdb",0)/*:site/*:categories/*:category[position() = 1 to 100]
> for $pe_1 in db:attribute("expdb",
> $cat_0/@*:id)/self::*:category/parent::*:interest/parent::*:profile/parent::*:person[3.0
> < count(*:profile/*:interest)]
> return element match { (element person { ($pe_1/*:name) }, element category
> { ($cat_0/*:name) }) }
>
> You can see that BaseX was able to use attribute index to optimize last
> query, reducing its execution time (by a lot!).
>
> My question is: what is the explanation for this behavior?
>
> Thank you in advance!
>
> Gabriel Tessarolli
>
> ---
> [1] http://www.xml-benchmark.org/
>
>
>
>