XQuery Syntax

XQuery elements, attributes, and variables must be valid XML names and follow case sensitivity.

XQuery Syntax Rules

XQuery follows case-sensitivity.
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, for example:. $bookstore
XQuery comments are delimited by (: and :), e.g. (: XQuery Comment :)

Example

Let's take an XML file 'books.xml' having the following data:

<bookstore>
<book category="Romantic">
<title lang="en">If she loves me</title>
<author>Ajeet Kumar</author>
<year>2014</year>
<price>150</price>
</book>
<book category="children">
<title lang="en">Harry Potter</title>
<author>J K. Rowling</author>
<year>2005</year>
<price>700</price>
</book>
<book category="programming">
<title lang="en">Let's C</title>
<author>Yashwant Kanetkar</author>
<year>2003</year>
<price>200</price>
</book>
</bookstore>

XQuery Conditional Expressions

The "If-Then-Else" conditional statement is allowed in XQuery.

XQuery statement:

books.xqy

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>

How to run

Create a Java based XQuery executor program to read the books.xqy, passes it to the XQuery expression processor, and executes the expression. After that the result will be displayed.

XQueryTester.java

import java.io.File;
import java.io.FileInputStream;
import java.io.FileNotFoundException;
import java.io.InputStream;
import javax.xml.xquery.XQConnection;
import javax.xml.xquery.XQDataSource;
import javax.xml.xquery.XQException;
import javax.xml.xquery.XQPreparedExpression;
import javax.xml.xquery.XQResultSequence;
import com.saxonica.xqj.SaxonXQDataSource;
public class XQueryTester {
   public static void main(String[] args){
      try {
         execute();
      }
      catch (FileNotFoundException e) {
         e.printStackTrace();
      }      
      catch (XQException e) {
         e.printStackTrace();
      }
   }
   private static void execute() throws FileNotFoundException, XQException{
      InputStream inputStream = new FileInputStream(new File("courses.xqy"));
      XQDataSource ds = new SaxonXQDataSource();
      XQConnection conn = ds.getConnection();
      XQPreparedExpression exp = conn.prepareExpression(inputStream);
      XQResultSequence result = exp.executeQuery();
       while (result.next()) {
         System.out.println(result.getItemAsString(null));
      }
   }	
}

Execute XQuery against XML

Put the above three files to a same location. We put them on desktop in a folder name XQuery6.

Compile XQueryTester.java using console. You must have JDK 1.5 or later installed on your computer and classpaths are configured.

Compile:

javac XQueryTester.java

Execute:

java XQueryTester

Output:

XQuery Comparisons

There are two types for comparing values in XQuery.

General Comparison: =, !=, <, <=, >, >=
Value Comparison: eq, ne, lt, le, gt, ge

Difference between general comparison and value comparison

It can be explained by an example. The following expression returns true if any q attributes have a value greater than 100.

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:

download this example

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