XQuery is case-sensitive and XQuery elements, attributes, and variables must be valid XML names.
XQuery Basic Syntax Rules
Some basic syntax rules:
- XQuery is case-sensitive
- XQuery elements, attributes, and variables must be valid XML names
- An XQuery string value can be in single or double quotes
- An XQuery variable is defined with a $ followed by a name, e.g. $bookstore
- XQuery comments are delimited by (: and :), e.g. (: XQuery Comment :)
The XML Example Document
We will use the "books.xml" document in the examples below (same XML file as in the previous chapters).
XQuery Conditional Expressions
"If-Then-Else" expressions are allowed in XQuery.
Look at the following example:
for $x in doc("books.xml")/bookstore/book
return if ($x/@category="CHILDREN")
then <child>{data($x/title)}</child>
else <adult>{data($x/title)}</adult>
Notes on the "if-then-else" syntax: parentheses around the if expression are required. else is required, but it can be just else ().
The result of the example above will be:
<adult>Everyday Italian</adult>
<child>Harry Potter</child>
<adult>XQuery Kick Start</adult>
<adult>Learning XML</adult>
XQuery Comparisons
In XQuery there are two ways of comparing values.
1. General comparisons: =, !=, <, <=, >, >=
2. Value comparisons: eq, ne, lt, le, gt, ge
The difference between the two comparison methods are shown below.
The following expression returns true if any q attributes have a value greater than 10:
$bookstore//book/@q > 10
The following expression returns true if there is only one q attribute returned by the expression, and its value is greater than 10. If more than one q is returned, an error occurs:
$bookstore//book/@q gt 10
