Sort a sequence of items.
A SortExpr sorts a sequence of items that is specified as
the expression to the left of the keywords sort by according to an
ordering expression, the SortSpecList. The result of
evaluating the expression that precedes the keywords sort by is
the input sequence. The sort result is the output
sequence.
The items of the input sequence are reordered according to the ordering
expressions in the SortSpecList. If there is more than one
ordering expression, then the first one is the primary sort criterion and the
other expressions are then processed from left to right. For each ordering
expression you can specify a sort direction, either ascending or
descending, with ascending as default.
For the sort operation to succeed, a common supertype of each ordering
expression is determined which is used for sorting. Each expression must return
not more than one item per object to be sorted. Also the comparison operator
gt must be defined for this type, otherwise an error is
raised.
Using the keyword stable does not have any effect and so the
keyword can be left out.
Sort all books that cost less than 50 dollars by first author and title:
declare namespace xs="http://www.w3.org/2001/XMLSchema" for $a in input()/bib/book where xs:decimal($a/price) < 50 return $a sort by (author[1]/last, title)
The input sequence comprises all book
elements that cost less than 50 dollars. The primary sort criterion is
author[1]/last, so the input sequence is ordered by the
last child element of the first
author element. Within each
author group, the input sequence is ordered by the
title element.
The following construct(s) refer to this construct:
