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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 :)

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>Learning XML</adult>
<adult>XQuery Kick Start</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