411 REFERENCE · Wikibooks
XQuery/Ah-has
Reference material by Wikibooks contributors. This retains its source identity and is not 411 news reporting.
Redundancy in Expressions
let $r := if ($x = 1) then true() else false();
better as
let $r := ($x = 1)
and
for $p in (0 to string-length($arg1)) return $p
better as
(0 to string-length($arg1))
and
for $i in (1 to 5)
return
for $j in (11 to 15)
return
($i, $j)
better as
for $i in (1 to 5), $j in (11 to 15)
return
($i, $j)
OR
for $i in (1 to 5)
for $j in (11 to 15)
return
($i, $j)
all three return
(1 11 1 12 1 13 1 14 1 15 2 11 2 12 2 13...)
XPath predicates clearer and faster than where clauses
for $x in //Page
where $x/heading = 1
return $x
better as
//Page[heading = 1]
Default values
if (exists($a)) then $a else "Default"
better as
($a,"Default") [1]
OR for a sequence of items
($list1, "Default"[empty($list1)])
OR another possible for a sequence
(,,)[not(position() = last() and not(last() = 1))]
any number of cascaded defaults can be handled this way.
compare with 'COALESCE' in SQL