XQuery Syntax

From http://www.w3schools.com (Copyright Refsnes Data)

# XQuery Syntax

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.

Look at the following XQuery expressions:

    $bookstore//book/@q > 10

    The expression above returns true if any q attributes
    have values greater than 10.

    $bookstore//book/@q gt 10

    The expression above 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.

From http://www.w3schools.com (Copyright Refsnes Data)