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<h1>XQuery Syntax</h1>
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<p class="intro">XQuery is case-sensitive and XQuery elements, attributes, and variables must be valid XML names.</p>
<hr />
<h2>XQuery Basic Syntax Rules</h2>
<p>Some basic syntax rules:</p>
<ul>
<li>XQuery is case-sensitive</li>
<li>XQuery elements, attributes, and variables must be valid XML names</li>
<li>An XQuery string value can be in single or double quotes</li>
<li>An XQuery variable is defined with a $ followed by a name, e.g.
$bookstore</li>
<li>XQuery comments are delimited by (: and :), e.g. (: XQuery Comment :)</li>
</ul>
<hr />
<h2>XQuery Conditional Expressions</h2>
<p>"If-Then-Else" expressions are allowed in XQuery.</p>
<p>Look at the following example:</p>
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<pre>for $x in doc("books.xml")/bookstore/book
return <span class="insert">if (</span>$x/@category="CHILDREN"<span class="insert">)</span>
<span class="insert">then</span> <child>{data($x/title)}</child>
<span class="insert">else</span> <adult>{data($x/title)}</adult></pre>
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<p><b>Notes on the "if-then-else" syntax:</b> parentheses around the if expression
are required. else is required, but it can be just else ().</p>
<p>The result of the example above will be:</p>
<table width="100%" border="1" class="ex" cellspacing="0" id="table16">
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<td>
<pre><adult>Everyday Italian</adult>
<child>Harry Potter</child>
<adult>Learning XML</adult>
<adult>XQuery Kick Start</adult></pre>
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<h2>XQuery Comparisons</h2>
<p>In XQuery there are two ways of comparing values.</p>
<p>1. General comparisons: =, !=, <, <=, >, >=</p>
<p>2. Value comparisons: eq, ne, lt, le, gt, ge</p>
<p>The difference between the two comparison methods are shown below.</p>
<p>Look at the following XQuery expressions:</p>
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<pre><span class="insert">$bookstore//book/@q > 10</span></pre>
<pre>The expression above returns true if any q attributes
have values greater than 10.</pre>
<pre><span class="insert">$bookstore//book/@q gt 10</span></pre>
<pre>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.</pre>
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