Changes

for $i in 1 to 10

return 6

==Variable Inlining==

(: rewritten to :)

'Results: ' || count(//nodes)

As the example shows, variable declarations might be located in the query prolog and in FLWOR expressions. They may also occur (and be inlined) in {{Code|try}}/{{Code|catch}}, {{Code|switch}} or {{Code|typeswitch}} expressions.

for $n in 1 to 5

return $n + 1

Subsequent rewritings might result in query plans that differ a lot from the original query. As this might complicate debugging, you can disable function inling during development by setting {{Option|INLINELIMIT}} to {{Code|0}}.

(: further rewritten to :)

2, 4

Folds are unrolled, too:

let $f := function($a, $b) { $a * $b }

return $f($f($f($f(1, 2), 3), 4), 5)

The standard unroll limit is <code>5</code>. It can be adjusted with the {{Option|UNROLLLIMIT}} option, e.g. via a pragma:

...

db:get('db10')//*[text() = 'abc'],

The last example indicates that index rewritings might be triggered by unrolling loops with paths on database nodes.

(: rewritten to :)

doc('addressbook.xml')/descendant::city

…unless the last step does not contain a positional predicate:

<syntaxhighlight lang="xquery">

doc('addressbook.xml')//city[1]

As the positional test refers to the city child step, a rewritten query would yield different steps.

(: rewritten to :)

a/b/c[d]

Names of nodes can be specified via name tests or predicates. If names are e.g. supplied via external variables, the predicates can often be dissolved:

(: rewritten to :)

db:get('addressbook')/descendant::city

==FLWOR Rewritings==

(: the remaining clauses are merged and rewritten to a simple map :)

(1 to 10)[. > 3] ! (. + 2)

==Static Typing==

for $i in 1 to 5

return 'number'

==Pure Logic==

(: rewritten to :)

('a', '')[.]

Boolean algebra (and set theory) comes with a set of laws that can all be applied to XQuery expressions.

(: rewritten to :)

231

;Return distinct values

(: rewritten to :)

('Muslim', 'Roman Catholic', 'Albanian Orthodox', ...)

==Index Rewritings==

(: rewritten to :)

db:text('factbook', 'Shenzhen')/parent::name

Multiple element names and query strings can be supplied in a path:

(: rewritten to :)

db:text('factbook', ('Jewish', 'Muslim'))/(parent::*:ethnicgroups | parent::*:religions)/parent::*

If multiple candidates for index access are found, the database statistics (if available) are consulted to choose the cheapest candidate:

(: rewritten to :)

db:text('factbook', 'Greeks')/parent::ethnicgroups/parent::country[religions = 'Muslim']

If index access is possible within more complex FLWOR expressions, only the paths will be rewritten:

order by $country/name[1]

return element { replace($country/@name, ' ', '') } {}

The [https://projects.cwi.nl/xmark/ XMark XML Benchmark] comes with sample auction data and a bunch of queries, some of which are suitable for index rewritings:

(: rewritten to :)

db:attribute('xmark', 'person0')/self::attribute(id)/parent::person/name/text()

;XMark Query 8

)

}</item>

If the accessed database is not known at compile time, or if you want to give a predicate preference to another one, you can [[Indexes#Enforce Rewritings|enforce index rewritings]].

let $input2 := file:read-text-lines('huge2.txt')

return $input1[not(. = $input2)]

=Changelog=