Re: [Exist-open] "limit" and "order by rand" with XQuery

[Wolfgang M. <wol...@ex...>]

Hi,

> I'm new to XQuery and I wonder if it is possible to limit the number of
> result nodes in the XQuery instead of giving it as a parameter to the eXist
> method? Like "LIMIT 10" for example in sql.

1) You can use the item-at() function to access an item in a sequence. Using 
this, I can output the first 10 items of a sequence as follows:

let $hits := (for $c in /country order by $c/city return $c)
for $p in 1 to 10 return item-at($hits, $p)

2) the subsequence() function makes this even simpler:

let $hits := (for $c in /country order by $c/city return $c)
return subsequence($hits, 1, 10)

>   Then I wonder if it is possible to request random order, like "ORDER BY
> RAND()" in sql. preferably, this should be possible to do not only on top
> level but also in a hierarcy like "order by $a/country ascending, order by
> random" that would mean the list would definitely be ordered by country
> names. However within next level (if there are duplicate country names but
> different {$a/country/city}) the $a nodes wouldn't appear exactly as stored
> in the database, neither alphabetized but randomly.

By default, all XQuery sequences are returned in document order. To return 
sequence values in a random order, you could use order by with some 
randomized value, e.g. by calling java.lang.Math.random

xquery version "1.0";
declare namespace math="java:java.lang.Math";

let $hits := //SPEECH[LINE &= 'curse*']
for $item in $hits
order by math:random()
return $item

Wolfgang