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18 Using XQuery with Oracle XML DB

This chapter describes how to use the XQuery language with Oracle XML DB. It covers Oracle XML DB support for the language, including SQL functions XMLQuery and XMLTable and the SQL*Plus XQUERY command.

This chapter contains these topics:

Overview of XQuery in Oracle XML DB

Oracle XML DB support for the XQuery language is provided through a native implementation of SQL/XML functions XMLQuery and XMLTable. As a convenience, SQL*Plus command XQUERY is also provided, which lets you enter XQuery expressions directly — in effect, this command turns SQL*Plus into an XQuery command-line interpreter.

Oracle XML DB compiles XQuery expressions that are passed as arguments to SQL functions XMLQuery, XMLTable, XMLExists, and XMLCast. This compilation produces SQL query blocks and operator trees that use SQL/XML functions and XPath functions. A SQL statement that includes XMLQuery, XMLTable, XMLExists, or XMLCast is compiled and optimized as a whole, leveraging both relational database and XQuery-specific optimization technologies. Depending on the XML storage and indexing methods used, XPath functions can be further optimized. The resulting optimized operator tree is executed in a streaming fashion.

See Also:

Overview of the XQuery Language

Oracle XML DB supports the latest version of the XQuery language specification, W3C XQuery 1.0 Recommendation. This section presents a brief overview of the language. For more information, consult a recent book on the language or refer to the standards documents that define it, which are available at http://www.w3c.org.

Functional Language Based on Sequences

XQuery 1.0 is the W3C language designed for querying XML data. It is similar to SQL in many ways, but just as SQL is designed for querying structured, relational data, XQuery is designed especially for querying semi-structured, XML data from a variety of data sources. You can use XQuery to query XML data wherever it is found, whether it is stored in database tables, available through Web Services, or otherwise created on the fly. In addition to querying XML data, XQuery can be used to construct XML data. In this regard, XQuery can serve as an alternative or a complement to both XSLT and the other SQL/XML publishing functions, such as XMLElement.

XQuery builds on the Post-Schema-Validation Infoset (PSVI) data model, which unites the XML Information Set (Infoset) data model and the XML Schema type system. XQuery defines a new data model based on sequences: the result of each XQuery expression is a sequence. XQuery is all about manipulating sequences. This makes XQuery similar to a set-manipulation language, except that sequences are ordered and can contain duplicate items. XQuery sequences differ from the sequences in some other languages in that nested XQuery sequences are always flattened in their effect.

In many cases, sequences can be treated as unordered, to maximize optimization – where this is available, it is under your control. This unordered mode can be applied to join order in the treatment of nested iterations (for), and it can be applied to the treatment of XPath expressions (for example, in /a/b, the matching b elements can be processed without regard to document order).

An XQuery sequence consists of zero or more items, which can be either atomic (scalar) values or XML nodes. Items are typed using a rich type system that is based upon the types of XML Schema. This type system is a major change from that of XPath 1.0, which is limited to simple scalar types such as Boolean, number, and string.

XQuery is a functional language. As such, it consists of a set of possible expressions that are evaluated and return values (which, for XQuery, are sequences). As a functional language, XQuery is also referentially transparent, generally: the same expression evaluated in the same context returns the same value.

Exceptions to this desirable mathematical property include the following:

  • XQuery expressions that derive their value from interaction with the external environment. For example, an expression such as fn:current-time(...) or fn:doc(...) does not necessarily always return the same value, since it depends on external conditions that can change (the time changes; the content of the target document might change).

    In some cases, like that of fn:doc, XQuery is defined to be referentially transparent within the execution of a single query: within a query, each invocation of fn:doc with the same argument results in the same document.

  • XQuery expressions that are defined to be dependent on the particular XQuery language implementation. The result of evaluating such expressions might vary between implementations. Function fn:doc is an example of a function that is essentially implementation-defined.

Referential transparency applies also to XQuery variables: the same variable in the same context has the same value. Functional languages are like mathematics formalisms in this respect and unlike procedural, or imperative, programming languages. A variable in a procedural language is really a name for a memory location; it has a current value, or state, as represented by its content at any time. A variable in a declarative language such as XQuery is really a name for a static value.

XQuery Expressions

XQuery expressions are case-sensitive. The expressions include the following:

  • primary expression – literal, variable, or function application. A variable name starts with a dollar-sign ($) – for example, $foo. Literals include numerals, strings, and character or entity references.

  • XPath expression – Any XPath expression. The developing XPath 2.0 standard will be a subset of XQuery. XPath 1.0 is currently a subset, although XQuery uses a richer type system.

  • FLWOR expression – The most important XQuery expression, composed of the following, in order, from which FLWOR takes its name: for, let, where, order by, return.

  • XQuery sequence – The comma (,) constructor creates sequences. Sequence-manipulating functions such as union and intersect are also available. All XQuery sequences are effectively flat: a nested sequence is treated as its flattened equivalent. Thus, for instance, (1, 2, (3, 4, (5), 6), 7) is treated as (1, 2, 3, 4, 5, 6, 7). A singleton sequence, such as (42), acts the same in most XQuery contexts as does its single item, 42. Remember that the result of any XQuery expression is a sequence.

  • Direct (literal) constructions – XML element and attribute syntax automatically constructs elements and attributes: what you see is what you get. For example, the XQuery expression <a>33</a> constructs the XML element <a>33</a>.

  • Computed (dynamic) constructions – You can construct XML data at runtime using computed values. For example, the following XQuery expression constructs this XML data: <foo toto="5"><bar>tata titi</bar> why? </foo>.

    <foo>{attribute toto {2+3}, element bar {"tata", "titi"}, text {" why? "}</foo>
    

    In this example, element foo is a direct construction; the other constructions are computed. In practice, the arguments to computed constructors are not literals (such as toto and "tata"), but expressions to be evaluated (such as 2+3). Both the name and the value arguments of an element or attribute constructor can be computed. Braces ({, }) are used to mark off an XQuery expression to be evaluated.

  • Conditional expression – As usual, but remember that each part of the expression is itself an arbitrary expression. For instance, in this conditional expression, each of these subexpressions can be any XQuery expression: something, somethingElse, expression1, and expression2.

     if (something < somethingElse) then expression1 else expression2
    
  • Arithmetic, relational expression – As usual, but remember that each relational expression returns a (BooleanFoot 1 ) value. Examples:

    2 + 3
    42 < $a + 5
    (1, 4) = (1, 2)
    5 > 3 eq true()
    
  • Quantifier expression – Universal (every) and existential (some) quantifier functions provide shortcuts to using a FLWOR expression in some cases. Examples:

    every $foo in doc("bar.xml")//Whatever satisfies $foo/@bar > 42
    some $toto in (42, 5), $titi in (123, 29, 5) satisfies $toto = $titi
    
  • Regular expression – XQuery regular expressions are based on XML Schema 1.0 and Perl. (See Support for XQuery Functions and Operators.)

  • Type expression – An XQuery expression that represents an XQuery type. Examples: item(), node(), attribute(), element(), document-node(), namespace(), text(), xs:integer, xs:string.Foot 2 

    Type expressions can have occurrence indicators: ? (optional: zero or one), * (zero or more), + (one or more). Examples: document-node(element())*, item()+, attribute()?.

    XQuery also provides operators for working with types. These include cast as, castable as, treat as, instance of, typeswitch, and validate. For example, "42" cast as xs:integer is an expression whose value is the integer 2. (It is not, strictly speaking, a type expression, because its value does not represent a type.)

FLWOR Expressions

As for XQuery in general, there is a lot to learn about FLWOR expressions. This section provides only a brief overview.

FLWOR is the most general expression syntax in XQuery. FLWOR (pronounced "flower") stands for for, let, where, order by, and return. A FLWOR expression has at least one for or let clause and a return clause; single where and order by clauses are optional.

  • for – Bind one or more variables each to any number of values, in turn. That is, for each variable, iterate, binding the variable to a different value for each iteration.

    At each iteration, the variables are bound in the order they appear, so that the value of a variable $earlier that is listed before a variable $later in the for list, can be used in the binding of variable $later. For example, during its second iteration, this expression binds $i to 4 and $j to 6 (2+4):

     for $i in (3, 4), $j in ($i, 2+$i)
    
  • let – Bind one or more variables.

    Just as with for, a variable can be bound by let to a value computed using another variable that is listed previously in the binding list of the let (or an enclosing for or let). For example, this expression binds $j to 5 (3+2):

    let $i := 3, $j := $i + 2
    
  • where – Filter the for and let variable bindings according to some condition. This is similar to a SQL WHERE clause.

  • order by – Sort the result of where filtering.

  • return – Construct a result from the ordered, filtered values. This is the result of the FLWOR expression as a whole. It is a flattened sequence.

Expressions for and let function similarly to a SQL FROM clause; where acts like a SQL WHERE clause; order by is similar to ORDER BY in SQL; and return is like SELECT in SQL. In other words, except for the two keywords whose names are the same in both languages (where, order by), FLWOR clause order is more or less opposite to the SQL clause order, but the meanings of the corresponding clauses are quite similar.

Note that using a FLWOR expression (with order by) is the only way to construct a sequence in any order other than document order.

SQL Functions XMLQUERY and XMLTABLE

SQL functions XMLQuery and XMLTable are defined by the SQL/XML standard as a general interface between the SQL and XQuery languages. As is the case for the other SQL/XML functions, XMLQuery and XMLTable let you take advantage of the power and flexibility of both SQL and XML. Using these functions, you can construct XML data using relational data, query relational data as if it were XML, and construct relational data from XML data.

Both XMLQuery and XMLTable evaluate an XQuery expression. In the XQuery language, an expression always returns a sequence of items. Function XMLQuery aggregates the items in this sequence to return a single XML document or fragment. Function XMLTable returns a SQL table whose rows each contain one item from the XQuery sequence.

The SQL/XML standard is ISO/IEC 9075–14:2006(E), Information technology – Database languages – SQL – Part 14: XML-Related Specifications (SQL/XML). As part of the SQL standard, it is aligned with SQL:2003. It is being developed under the auspices of these two standards bodies:

This SQL/XML standardization process is ongoing. Please refer to http://www.sqlx.org for the latest information about XMLQuery and XMLTable.

See Also:

XMLQUERY SQL Function in Oracle XML DB

You use SQL function XMLQuery to construct or query XML data. This function takes as arguments an XQuery expression, as a string literal, and an optional XQuery context item, as a SQL expression. The context item establishes the XPath context in which the XQuery expression is evaluated. Additionally, XMLQuery accepts as arguments any number of SQL expressions whose values are bound to XQuery variables during the XQuery expression evaluation. The function returns the result of evaluating the XQuery expression, as an XMLType instance.

Figure 18-1 XMLQUERY Syntax

Description of Figure 18-1 follows
Description of "Figure 18-1 XMLQUERY Syntax"

XML_passing_clause ::= 

Description of xml_passing_clause.gif follows
Description of the illustration xml_passing_clause.gif

  • XQuery_string is a complete XQuery expression, possibly including a prolog, as a literal string.

  • The XML_passing_clause is the keyword PASSING followed by one or more SQL expressions (expr) that each return an XMLType instance or an instance of a SQL scalar data type (that is, not an object or collection data type). Each expression (expr) can be a table or view column value, a PL/SQL variable, or a bind variables with proper casting. All but possibly one of the expressions must each be followed by the keyword AS and an XQuery identifier. The result of evaluating each expr is bound to the corresponding identifier for the evaluation of XQuery_string. If there is an expr that is not followed by an AS clause, then the result of evaluating that expr is used as the context item for evaluating XQuery_string. Oracle XML DB supports only passing BY VALUE, not passing BY REFERENCE, so the clause BY VALUE is implicit and can be omitted.

  • RETURNING CONTENT indicates that the value returned by an application of XMLQuery is an instance of parameterized XML type XML(CONTENT), not parameterized type XML(SEQUENCE). It is a document fragment that conforms to the extended Infoset data model. As such, it is a single document node with any number of children. The children can each be of any XML node type; in particular, they can be text nodes.

    Oracle XML DB supports only the RETURNING CONTENT clause of SQL/XML function XMLQuery; it does not support the RETURNING SEQUENCE clause.

You can pass an XMLType column, table, or view as the context-item argument to function XMLQuery — see, for example, Example 18-8. To query a relational table or view as if it were XML, without having to first create a SQL/XML view on top of it, use XQuery function ora:view within an XQuery expression — see, for example, Example 18-6.

See Also:

XMLTABLE SQL Function in Oracle XML DB

You use SQL function XMLTable to decompose the result of an XQuery-expression evaluation into the relational rows and columns of a new, virtual table. You can then insert the virtual table into a pre-existing database table, or you can query it using SQL — in a join expression, for example (see Example 18-9). You use XMLTable in a SQL FROM clause.

Figure 18-2 XMLTABLE Syntax

Description of Figure 18-2 follows
Description of "Figure 18-2 XMLTABLE Syntax"

XML_namespaces_clause ::= 

Description of xml_namespaces_clause.gif follows
Description of the illustration xml_namespaces_clause.gif

XMLTABLE_options ::= 

Description of xmltable_options.gif follows
Description of the illustration xmltable_options.gif

XML_passing_clause ::= 

Description of xml_passing_clause.gif follows
Description of the illustration xml_passing_clause.gif

XML_table_column ::= 

Description of xml_table_column.gif follows
Description of the illustration xml_table_column.gif

  • XQuery_string is a complete XQuery expression, possibly including a prolog, as a literal string. The value of the expression serves as input to the XMLTable function; it is this XQuery result that is decomposed and stored as relational data.

  • The optional XMLNAMESPACES clause contains XML namespace declarations that are referenced by XQuery_string and by the XPath expression in the PATH clause of XML_table_column.

  • The XML_passing_clause is the keyword PASSING followed by one or more SQL expressions (expr) that each return an XMLType instance or an instance of a SQL scalar data type (that is, not an object or collection data type). Each expression (expr) can be a table or view column value, a PL/SQL variable, or a bind variables with proper casting. All but possibly one of the expressions must each be followed by the keyword AS and an XQuery identifier. The result of evaluating each expr is bound to the corresponding identifier for the evaluation of XQuery_string. If there is an expr that is not followed by an AS clause, then the result of evaluating that expr is used as the context item for evaluating XQuery_string. Oracle XML DB supports only passing BY VALUE, not passing BY REFERENCE, so the clause BY VALUE is implicit and can be omitted.

  • The optional COLUMNS clause defines the columns of the virtual table to be created by XMLTable.

    • If you omit the COLUMNS clause, then XMLTable returns a row with a single XMLType pseudo-column, named COLUMN_VALUE.

    • FOR ORDINALITY specifies that column is to be a column of generated row numbers (SQL data type NUMBER). There must be at most one FOR ORDINALITY clause.

    • You must specify the datatype of each resulting column except the FOR ORDINALITY column. However, see next bullet.

    • When XMLTable is used with XML schema-based storage of XMLType, datatype is optional. If not present, the data type will be inferred from the XML schema. If Oracle XML DB is unable to determine the proper type for a node, a default type of VARCHAR2(4000) is used.

      This is an Oracle extension; in the SQL/XML standard, datatype is always required.

      Note:

      The inferred data type might change as the result of upgrading Oracle XML DB or applying a patch. In particular, a new release or patch set might be able to determine the data type when the previous release was unable to do so (and so defaulted to VARCHAR2(4000)). To protect against such an eventuality, specify an explicit data type with datatype.
    • The optional PATH clause specifies that the portion of the XQuery result that is addressed by XQuery expression string is to be used as the column content. You can use multiple PATH clauses to split the XQuery result into different virtual-table columns.

      If you omit PATH, then the XQuery expression column is assumed. For example, these two expressions are equivalent:

      XMLTable(... COLUMNS foo)
      XMLTable(... COLUMNS foo PATH 'FOO')
      
    • The optional DEFAULT clause specifies the value to use when the PATH expression results in an empty sequence (or NULL). Its expr is an XQuery expression that is evaluated to produce the default value.

See Also:

Note:

Prior to Oracle Database 10g Release 2, XMLSequence was used with SQL function table to do some of what can now be done better with standard function XMLTable. See Chapter 3, "Using Oracle XML DB" for examples.

When To Use XQuery

You can use XQuery to do many of the same things that you might do using the SQL/XML generation functions or XSLT; there is a great deal of overlap. The decision to use one or the other tool to accomplish a given task can be based on many considerations, most of which are not specific to Oracle Database. Please consult external documentation on this general question.

One general rule of thumb is that XQuery is often used when the focus is the world of XML data, while the SQL/XML generation functions (XMLElement, XMLAgg, and so on) are often used when the focus is the world of relational data.

Other things being equal, if a query constructs an XML document from fragments extracted from existing XML documents, then it is likely that an XQuery FLOWR expression will be simpler (simplifying code maintenance) than extracting scalar values from relational data and constructing appropriate XML data using SQL/XML generation functions. If, instead, a query constructs an XML document from existing relational data, the SQL/XML generation functions can often be more suitable.

With respect to Oracle XML DB, you can expect the same general level of performance using the SQL/XML generation functions as with XMLQuery and XMLTable — all are subject to rewrite optimizations.

Predefined Namespaces and Prefixes

The following namespaces and prefixes are predefined for use with XQuery in Oracle XML DB:

Table 18-1 Predefined Namespaces and Prefixes

Prefix Namespace Description

ora

http://xmlns.oracle.com/xdb

Oracle XML DB namespace

local

http://www.w3.org/2003/11/xpath-local-functions

XPath local function declaration namespace

fn

http://www.w3.org/2003/11/xpath-functions

XPath function namespace

xml

http://www.w3.org/XML/1998/namespace

XML namespace

xs

http://www.w3.org/2001/XMLSchema

XML Schema namespace

xsi

http://www.w3.org/2001/XMLSchema-instance

XML Schema instance namespace


You can use these prefixes in XQuery expressions without first declaring them in the XQuery-expression prolog. You can redefine any of them except xml in the prolog. All of these prefixes except ora are predefined in the XQuery standard.

Oracle XQuery Extension Functions

Oracle XML DB adds some XQuery functions to those provided in the W3C standard. These additional functions are in the Oracle XML DB namespace, http://xmlns.oracle.com/xdb, which uses the predefined prefix ora. This section describes these Oracle extension functions.

ora:contains XQuery Function

Syntax

ora:contains (input_text, text_query [, policy_name] [, policy_owner])

XPath function ora:contains can be used in an XPath expression inside an XQuery expression or in a call to SQL function existsNode, extract, or extractValue. It is used to restrict a structural search with a full-text predicate. Function ora:contains returns a positive integer when the input_text matches text_query (the higher the number, the more relevant the match), and zero otherwise. When used in an XQuery expression, the XQuery return type is xs:integer(); when used in an XPath expression outside of an XQuery expression, the XPath return type is number.

Argument input_text must evaluate to a single text node or an attribute. The syntax and semantics of text_query in ora:contains are the same as text_query in contains, with a few restrictions.

ora:matches XQuery Function

Syntax

ora:matches (target_string, match_pattern [, match_parameter])

XQuery function ora:matches lets you use a regular expression to match text in a string. It returns true() if its target_string argument matches its regular-expression match_pattern argument and false() otherwise. If target_string is the empty sequence, false() is returned. Optional argument match_parameter is a code that qualifies matching: case-sensitivity and so on.

The behavior of XQuery function ora:matches is the same as that of SQL condition REGEXP_LIKE, but the types of its arguments are XQuery types instead of SQL data types. The argument types are as follows:

  • target_stringxs:string?Foot 3 

  • match_patternxs:string

  • match_parameterxs:string

See Also:

Oracle Database SQL Language Reference for information about SQL condition REGEXP_LIKE

ora:replace XQuery Function

Syntax

ora:replace (target_string, match_pattern, replace_string [, match_parameter])

XQuery function ora:replace lets you use a regular expression to replace matching text in a string. Each occurrence in target_string that matches regular-expression match_pattern is replaced by replace_string. It returns the new string that results from the replacement. If target_string is the empty sequence, then the empty string ("") is returned. Optional argument match_parameter is a code that qualifies matching: case-sensitivity and so on.

The behavior of XQuery function ora:matches is the same as that of SQL function regexp_replace, but the types of its arguments are XQuery types instead of SQL data types. The argument types are as follows:

  • target_stringxs:string?Foot 4 

  • match_patternxs:string

  • replace_stringxs:string

  • match_parameterxs:string

In addition, ora:replace requires argument replace_string (it is optional in regexp_replace) and it does not use arguments for position and number of occurrences – search starts with the first character and all occurrences are replaced.

See Also:

Oracle Database SQL Language Reference for information about SQL function regexp_replace

ora:sqrt XQuery Function

Syntax

ora:sqrt (number)

XQuery function ora:sqrt returns the square root of its numerical argument, which can be of XQuery type xs:decimal, xs:float, or xs:double. The returned value is of the same XQuery type as the argument.

ora:view XQuery Function

Syntax

ora:view ([db-schema STRING,] db-table STRING)
RETURNS document-node(element())*Foot 5 

XQuery function ora:view lets you query existing database tables or views inside an XQuery expression, as if they were XML documents. In effect, ora:view creates XML views over the relational data, on the fly. You can thus use ora:view to avoid explicitly creating XML views on top of relational data.

The input parameters are as follows:

  • db-schema – An optional string literal that names a database schema.

  • db-table – A string literal naming a database table or view. If db-schema is present, then db-table is in database schema db-schema.

Function ora:view returns an unordered sequence of document nodes, one for each row of db-table. The SQL/XML standard is used to map each input row to the output XML document: relational column names become XML element names. Unless db-table is of type XMLType, the column elements derived from a given table row are wrapped together in a ROW element. In that case, the return type is, more precisely, document-node(element(ROW))*.

XMLQUERY and XMLTABLE Examples

XQuery is a very general and expressive language, and SQL functions XMLQuery, XMLTable, and XMLExists combine that power of expression and computation with the similar strengths of SQL. This section illustrates some of what you can do with these two SQL/XML functions. See "XMLEXISTS SQL Function" for information about XMLExists.

You will typically use XQuery with Oracle XML DB in the following ways. The examples here are organized to reflect these different uses.

Example 18-1 Creating Resources for Examples

This example creates repository resources that are used in some of the other examples.

DECLARE
  res BOOLEAN;
  empsxmlstring VARCHAR2(300):= 
    '<?xml version="1.0"?>
     <emps>
       <emp empno="1" deptno="10" ename="John" salary="21000"/>
       <emp empno="2" deptno="10" ename="Jack" salary="310000"/>
       <emp empno="3" deptno="20" ename="Jill" salary="100001"/>
     </emps>';
  empsxmlnsstring VARCHAR2(300):=
    '<?xml version="1.0"?>
     <emps xmlns="http://emp.com">
       <emp empno="1" deptno="10" ename="John" salary="21000"/>
       <emp empno="2" deptno="10" ename="Jack" salary="310000"/>
       <emp empno="3" deptno="20" ename="Jill" salary="100001"/>
     </emps>';
  deptsxmlstring VARCHAR2(300):=
    '<?xml version="1.0"?>
     <depts>
       <dept deptno="10" dname="Administration"/>
       <dept deptno="20" dname="Marketing"/>
       <dept deptno="30" dname="Purchasing"/>
     </depts>';
BEGIN
  res := DBMS_XDB.createResource('/public/emps.xml',   empsxmlstring);
  res := DBMS_XDB.createResource('/public/empsns.xml', empsxmlnsstring);
  res := DBMS_XDB.createResource('/public/depts.xml',  deptsxmlstring);
END;
/

XQuery Is About Sequences

It is important to keep in mind that XQuery is a general sequence-manipulation language. Its expressions and their results are not necessarily XML data. An XQuery sequence can contain items of any XQuery type, which includes numbers, strings, Boolean values, dates, as well as various types of XML node (document-node(), element(), attribute(), text(), namespace(), and so on). Example 18-2 provides a sampling.

Example 18-2 XMLQuery Applied to a Sequence of Items of Different Types

This example applies SQL function XMLQuery to an XQuery sequence that contains items of several different kinds:

  • an integer literal: 1

  • a arithmetic expression: 2 + 3

  • a string literal: "a"

  • a sequence of integers: 100 to 102

  • a constructed XML element node: <A>33</A>

This example also shows construction of a sequence using the comma operator (,) and parentheses ((, )) for grouping.

SELECT XMLQuery('(1, 2 + 3, "a", 100 to 102, <A>33</A>)'
                RETURNING CONTENT) AS output
  FROM DUAL;

OUTPUT
--------------------------
1 5 a 100 101 102<A>33</A>
 
1 row selected.

The sequence expression 100 to 102 evaluates to the sequence (100, 101, 102), so the argument to XMLQuery is a sequence that contains a nested sequence. The sequence argument is automatically flattened, as is always the case for XQuery sequences. The argument is, in effect, (1, 5, "a", 100, 101, 102, <A>33</A>).

Using XQuery to Query XML Data in Oracle XML DB Repository

This section presents examples of using XQuery with XML data in Oracle XML DB Repository. In Oracle XML DB, functions fn:doc and fn:collection return file and folder resources in the repository, respectively. Each example in this section uses XQuery function fn:doc to obtain a repository file that contains XML data, and then binds XQuery variables to parts of that data using for and let FLWOR-expression clauses.

Example 18-3 FLOWR Expression Using For, Let, Order By, Where, and Return

This example queries two XML-document resources in Oracle XML DB Repository: /public/emps.xml and /public/depts.xml. It illustrates the use of each of the possible FLWOR-expression clauses, as well as the use of fn:doc.

SELECT XMLQuery('for $e in doc("/public/emps.xml")/emps/emp
                 let $d :=
                   doc("/public/depts.xml")//dept[@deptno = $e/@deptno]/@dname
                 where $e/@salary > 100000
                 order by $e/@empno
                 return <emp ename="{$e/@ename}" dept="{$d}"/>'
                RETURNING CONTENT) FROM DUAL;

XMLQUERY('FOR$EINDOC("/PUBLIC/EMPS.XML")/EMPS/EMPLET$D:=DOC("/PUBLIC/DEPTS.XML")
--------------------------------------------------------------------------------
<emp ename="Jack" dept="Administration"></emp><emp ename="Jill" dept="Marketing"
></emp>
 
1 row selected.

In Example 18-3, the various FLWOR clauses perform these operations:

  • for iterates over the emp elements in /public/emps.xml, binding variable $e to the value of each such element, in turn. That is, it iterates over a general list of employees, binding $e to each employee.

  • let binds variable $d to a sequence consisting of all of the values of dname attributes of those dept elements in /public/emps.xml whose deptno attributes have the same value as the deptno attribute of element $e (this is a join operation). That is, it binds $d to the names of all of the departments that have the same department number as the department of employee $e. (It so happens that the dname value is unique for each deptno value in depts.xml.) Note that, unlike for, let never iterates over values; $d is bound only once in this example.

  • Together, for and let produce a stream of tuples ($e, $d), where $e represents an employee and $d represents the names of all of the departments to which that employee belongs —in this case, the unique name of the employee's unique department.

  • where filters this tuple stream, keeping only tuples with employees whose salary is greater than 100,000.

  • order by sorts the filtered tuple stream by employee number, empno (in ascending order, by default).

  • return constructs emp elements, one for each tuple. Attributes ename and dept of these elements are constructed using attribute ename from the input and $d, respectively. Note that the element and attribute names emp and ename in the output have no necessary connection with the same names in the input document emps.xml.

Example 18-4 also uses each of the FLWOR-expression clauses. In addition, it demonstrates the use of other XQuery functions, besides fn:doc.

Example 18-4 FLOWR Expression Using Built-In Functions

This example shows the use of XQuery functions doc, count, avg, and integer, which are in the namespace for built-in XQuery functions, http://www.w3.org/2003/11/xpath-functions. This namespace is bound to the prefix fn.

SELECT XMLQuery('for $d in fn:doc("/public/depts.xml")/depts/dept/@deptno
                 let $e := fn:doc("/public/emps.xml")/emps/emp[@deptno = $d]
                 where fn:count($e) > 1
                 order by fn:avg($e/@salary) descending
                 return
                   <big-dept>{$d,
                              <headcount>{fn:count($e)}</headcount>,
                              <avgsal>{xs:integer(fn:avg($e/@salary))}</avgsal>}
                   </big-dept>'
                RETURNING CONTENT) FROM DUAL;

XMLQUERY('FOR$DINFN:DOC("/PUBLIC/DEPTS.XML")/DEPTS/DEPT/@DEPTNOLET$E:=FN:DOC("/P
--------------------------------------------------------------------------------
<big-dept deptno="10"><headcount>2</headcount><avgsal>165500</avgsal></big-dept>
 
1 row selected.

In Example 18-4, the various FLWOR clauses perform these operations:

  • for iterates over deptno attributes in input document /public/depts.xml, binding variable $d to the value of each such attribute, in turn.

  • let binds variable $e to a sequence consisting of all of the emp elements in input document /public/emps.xml whose deptno attributes have value $d (this is a join operation).

  • Together, for and let produce a stream of tuples ($d, $e), where $d represents a department number and $e represents the set of employees in that department.

  • where filters this tuple stream, keeping only tuples with more than one employee.

  • order by sorts the filtered tuple stream by average salary in descending order. The average is computed by applying XQuery function avg (in namespace fn) to the values of attribute salary, which is attached to the emp elements of $e.

  • return constructs big-dept elements, one for each tuple produced by order by. The text() node of big-dept contains the department number, bound to $d. A headcount child element contains the number of employees, bound to $e, as determined by XQuery function count. An avgsal child element contains the computed average salary.

Using ora:view to Query Relational Data in XQuery Expressions

This section presents examples of using Oracle XQuery function ora:view to query relational data as if it were XML data, from within an XQuery expression.

Example 18-5 Using ora:view to Query Relational Tables as XML Views

This example uses Oracle XQuery function ora:view in a FLWOR expression to query two relational tables, regions and countries joining. Both tables belong to sample database schema hr. The example also passes scalar SQL value Asia to XQuery variable $regionname. Any SQL expression can be evaluated to produce a value passed to XQuery using PASSING. In this case, the value comes from a SQL*Plus variable, REGION. You must cast the value to the scalar SQL data type expected, in this case, VARCHAR2(40).

DEFINE REGION = 'Asia'
SELECT XMLQuery('for $i in ora:view("REGIONS"), $j in ora:view("COUNTRIES")
                   where $i/ROW/REGION_ID = $j/ROW/REGION_ID
                     and $i/ROW/REGION_NAME = $regionname
                   return $j'
                PASSING CAST('&REGION' AS VARCHAR2(40)) AS "regionname"
                RETURNING CONTENT) AS asian_countries
  FROM DUAL;

This produces the following result. (The result is shown here pretty-printed, for clarity.)

ASIAN_COUNTRIES
-----------------------------------------
<ROW>
  <COUNTRY_ID>AU</COUNTRY_ID>
  <COUNTRY_NAME>Australia</COUNTRY_NAME>
  <REGION_ID>3</REGION_ID>
</ROW>
<ROW>
  <COUNTRY_ID>CN</COUNTRY_ID>
  <COUNTRY_NAME>China</COUNTRY_NAME>
  <REGION_ID>3</REGION_ID>
</ROW>
<ROW>
  <COUNTRY_ID>HK</COUNTRY_ID>
  <COUNTRY_NAME>HongKong</COUNTRY_NAME>
  <REGION_ID>3</REGION_ID>
</ROW>
<ROW>
  <COUNTRY_ID>IN</COUNTRY_ID>
  <COUNTRY_NAME>India</COUNTRY_NAME>
  <REGION_ID>3</REGION_ID>
</ROW>
<ROW>
  <COUNTRY_ID>JP</COUNTRY_ID>
  <COUNTRY_NAME>Japan</COUNTRY_NAME>
  <REGION_ID>3</REGION_ID>
</ROW>
<ROW>
  <COUNTRY_ID>SG</COUNTRY_ID>
  <COUNTRY_NAME>Singapore</COUNTRY_NAME>
  <REGION_ID>3</REGION_ID>
</ROW>
 
1 row selected.

In Example 18-5, the various FLWOR clauses perform these operations:

  • for iterates over sequences of XML elements returned by calls to ora:view. In the first call, each element corresponds to a row of relational table regions and is bound to variable $i. Similarly, in the second call to ora:view, $j is bound to successive rows of table countries. Since regions and countries are not XMLType tables, the top-level element corresponding to a row in each table is ROW (a wrapper element). Iteration over the row elements is unordered.

  • where filters the rows from both tables, keeping only those pairs of rows whose region_id is the same for each table (it performs a join on region_id) and whose region_name is Asia.

  • return returns the filtered rows from the countries table as an XML document containing XML fragments with ROW as their top-level element.

Example 18-6 uses ora:view within nested FLWOR expressions.

Example 18-6 Using ora:view in a Nested FLWOR Query

This query is an example of using nested FLWOR expressions. It accesses relational table warehouses, which is in sample database schema oe, and relational table locations, which is in sample database schema hr. To run this example as user oe, you must first connect as user hr and grant permission to user oe to perform SELECT operations on table locations. The two-argument form of ora:view is used here, to specify the database schema (first argument) in addition to the table (second argument).

CONNECT hr
Enter password: password

Connected.

GRANT SELECT ON LOCATIONS TO OE
/
CONNECT oe
Enter password: password

Connected.

SELECT XMLQuery(
         'for $i in ora:view("OE", "WAREHOUSES")/ROW
          return <Warehouse id="{$i/WAREHOUSE_ID}">
                 <Location>
                   {for $j in ora:view("HR", "LOCATIONS")/ROW 
                    where $j/LOCATION_ID eq $i/LOCATION_ID 
                    return ($j/STREET_ADDRESS, $j/CITY, $j/STATE_PROVINCE)}
                 </Location>    
                 </Warehouse>'
         RETURNING CONTENT) FROM DUAL;

This produces the following result. (The result is shown here pretty-printed, for clarity.)

XMLQUERY('FOR$IINORA:VIEW("OE","WAREHOUSES")/ROWRETURN<WAREHOUSEID="{$I/WAREHOUS
--------------------------------------------------------------------------------
<Warehouse id="1">
  <Location>
    <STREET_ADDRESS>2014 Jabberwocky Rd</STREET_ADDRESS>
    <CITY>Southlake</CITY>
    <STATE_PROVINCE>Texas</STATE_PROVINCE>
  </Location>
</Warehouse>
<Warehouse id="2">
  <Location>
    <STREET_ADDRESS>2011 Interiors Blvd</STREET_ADDRESS>
    <CITY>South San Francisco</CITY>
    <STATE_PROVINCE>California</STATE_PROVINCE>
  </Location>
</Warehouse>
<Warehouse id="3">
  <Location>
    <STREET_ADDRESS>2007 Zagora St</STREET_ADDRESS>
    <CITY>South Brunswick</CITY>
    <STATE_PROVINCE>New Jersey</STATE_PROVINCE>
  </Location>
</Warehouse>
<Warehouse id="4">
  <Location>
    <STREET_ADDRESS>2004 Charade Rd</STREET_ADDRESS>
    <CITY>Seattle</CITY>
    <STATE_PROVINCE>Washington</STATE_PROVINCE>
  </Location>
</Warehouse>
<Warehouse id="5">
  <Location>
    <STREET_ADDRESS>147 Spadina Ave</STREET_ADDRESS>
    <CITY>Toronto</CITY>
    <STATE_PROVINCE>Ontario</STATE_PROVINCE>
  </Location>
</Warehouse>
<Warehouse id="6">
  <Location>
    <STREET_ADDRESS>12-98 Victoria Street</STREET_ADDRESS>
    <CITY>Sydney</CITY>
    <STATE_PROVINCE>New South Wales</STATE_PROVINCE>
  </Location>
</Warehouse>
<Warehouse id="7">
  <Location>
    <STREET_ADDRESS>Mariano Escobedo 9991</STREET_ADDRESS>
    <CITY>Mexico City</CITY>
    <STATE_PROVINCE>Distrito Federal,</STATE_PROVINCE>
  </Location>
</Warehouse>
<Warehouse id="8">
  <Location>
    <STREET_ADDRESS>40-5-12 Laogianggen</STREET_ADDRESS>
    <CITY>Beijing</CITY>
  </Location>
</Warehouse>
<Warehouse id="9">
  <Location>
    <STREET_ADDRESS>1298 Vileparle (E)</STREET_ADDRESS>
    <CITY>Bombay</CITY>
    <STATE_PROVINCE>Maharashtra</STATE_PROVINCE>
  </Location>
</Warehouse>
 
1 row selected.

In Example 18-6, the various FLWOR clauses perform these operations:

  • The outer for iterates over the sequence of XML elements returned by ora:view: each element corresponds to a row of relational table warehouses and is bound to variable $i. Since warehouses is not an XMLType table, the top-level element corresponding to a row is ROW. The iteration over the row elements is unordered.

  • The inner for iterates, similarly, over a sequence of XML elements returned by ora:view: each element corresponds to a row of relational table locations and is bound to variable $j.

  • where filters the tuples ($i, $j), keeping only those whose location_id child is the same for $i and $j (it performs a join on location_id).

  • The inner return constructs an XQuery sequence of elements STREET_ADDRESS, CITY, and STATE_PROVINCE, all of which are children of locations-table ROW element $j; that is, they are the values of the locations-table columns of the same name.

  • The outer return wraps the result of the inner return in a Location element, and wraps that in a Warehouse element. It provides the Warehouse element with an id attribute whose value comes from the warehouse_id column of table warehouses.

See Also:

Example 18-15 for the EXPLAIN PLAN of Example 18-6

Example 18-7 Using ora:view with XMLTable to Query a Relational Table as XML

In this example, SQL function XMLTable is used to decompose the result of an XQuery query to virtual relational data. The XQuery expression used in this example is identical to the one used in Example 18-6; the result of evaluating the XQuery expression is a sequence of Warehouse elements. Function XMLTable produces a virtual relational table whose rows are those Warehouse elements. More precisely, the value of pseudocolumn COLUMN_VALUE for each virtual-table row is an XML fragment (of type XMLType) with a single Warehouse element.

SELECT * 
  FROM XMLTable(
         'for $i in ora:view("OE", "WAREHOUSES")/ROW
          return <Warehouse id="{$i/WAREHOUSE_ID}">
                   <Location>
                     {for $j in ora:view("HR", "LOCATIONS")/ROW
                      where $j/LOCATION_ID eq $i/LOCATION_ID 
                      return ($j/STREET_ADDRESS, $j/CITY, $j/STATE_PROVINCE)} 
                   </Location>
                 </Warehouse>'); 

This produces the same result as Example 18-6, except that each Warehouse element is output as a separate row, instead of all Warehouse elements being output together in a single row.

COLUMN_VALUE
--------------------------------------------------------
<Warehouse id="1">
  <Location>
    <STREET_ADDRESS>2014 Jabberwocky Rd</STREET_ADDRESS>
    <CITY>Southlake</CITY>
    <STATE_PROVINCE>Texas</STATE_PROVINCE>
  </Location>
</Warehouse>
<Warehouse id="2">
  <Location>
    <STREET_ADDRESS>2011 Interiors Blvd</STREET_ADDRESS>
    <CITY>South San Francisco</CITY>
    <STATE_PROVINCE>California</STATE_PROVINCE>
  </Location>
</Warehouse>
. . .
 
9 rows selected.

See Also:

Example 18-16 for the EXPLAIN PLAN of Example 18-7

Using XQuery with XMLType Data

This section presents examples of using XQuery with XMLType relational data.

Example 18-8 Using XMLQuery with PASSING Clause, to Query an XMLType Column

This example passes an XMLType column, oe.warehouse_spec, as context item to XQuery, using function XMLQuery with the PASSING clause. It constructs a Details element for each of the warehouses whose area is greater than 80,000: /Warehouse/ Area > 80000.

SELECT warehouse_name, 
       XMLQuery(
         'for $i in /Warehouse 
          where  $i/Area > 80000 
          return <Details>
                   <Docks num="{$i/Docks}"/>
                   <Rail>{if ($i/RailAccess = "Y") then "true" else "false"}
                   </Rail>
                 </Details>'
         PASSING warehouse_spec RETURNING CONTENT) big_warehouses
  FROM warehouses;

This produces the following output:

WAREHOUSE_NAME
--------------
BIG_WAREHOUSES
--------------
Southlake, Texas
 
 
San Francisco
 
 
New Jersey
<Details><Docks num=""></Docks><Rail>false</Rail></Details>
 
Seattle, Washington
<Details><Docks num="3"></Docks><Rail>true</Rail></Details>
 
Toronto
 
 
Sydney
 
 
Mexico City
 
 
Beijing
 
 
Bombay
 
 
9 rows selected.

In Example 18-8, function XMLQuery is applied to the warehouse_spec column in each row of table warehouses. The various FLWOR clauses perform these operations:

  • for iterates over the Warehouse elements in each row of column warehouse_spec (the passed context item): each such element is bound to variable $i, in turn. The iteration is unordered.

  • where filters the Warehouse elements, keeping only those whose Area child has a value greater than 80,000.

  • return constructs an XQuery sequence of Details elements, each of which contains a Docks and a Rail child elements. The num attribute of the constructed Docks element is set to the text() value of the Docks child of Warehouse. The text() content of Rail is set to true or false, depending on the value of the RailAccess attribute of element Warehouse.

The SELECT statement applies to each row in table warehouses. The XMLQuery expression returns the empty sequence for those rows that do not match the XQuery expression. Only the warehouses in New Jersey and Seattle satisfy the XQuery query, so they are the only warehouses for which <Details>...</Details> is returned.

Example 18-9 Using XMLTable with XML Schema-Based Data

This example uses SQL function XMLTable to query an XMLType table, hr.purchaseorder, which contains XML Schema-based data. It uses the PASSING clause to provide the purchaseorder table as the context item for the XQuery-expression argument to XMLTable. Pseudocolumn COLUMN_VALUE of the resulting virtual table holds a constructed element, A10po, which contains the Reference information for those purchase orders whose CostCenter element has value A10 and whose User element has value SMCCAIN. The query performs a join between the virtual table and database table purchaseorder.

SELECT xtab.COLUMN_VALUE
  FROM purchaseorder, XMLTable('for $i in /PurchaseOrder
                                where $i/CostCenter eq "A10"
                                  and $i/User eq "SMCCAIN"
                                return <A10po pono="{$i/Reference}"/>'
                               PASSING OBJECT_VALUE) xtab;
 
COLUMN_VALUE
---------------------------------------------------
<A10po pono="SMCCAIN-20021009123336151PDT"></A10po>
<A10po pono="SMCCAIN-20021009123336341PDT"></A10po>
<A10po pono="SMCCAIN-20021009123337173PDT"></A10po>
<A10po pono="SMCCAIN-20021009123335681PDT"></A10po>
<A10po pono="SMCCAIN-20021009123335470PDT"></A10po>
<A10po pono="SMCCAIN-20021009123336972PDT"></A10po>
<A10po pono="SMCCAIN-20021009123336842PDT"></A10po>
<A10po pono="SMCCAIN-20021009123336512PDT"></A10po>
<A10po pono="SMCCAIN-2002100912333894PDT"></A10po>
<A10po pono="SMCCAIN-20021009123337403PDT"></A10po>
 
10 rows selected.

The PASSING clause of function XMLTable passes the OBJECT_VALUE of XMLType table purchaseorder, to serve as the XPath context. This means that the XMLTable expression depends on the purchaseorder table. Because of this, table purchaseorder must appear before the XMLTable expression in the FROM list. This is a general requirement in any situation involving data dependence.

Note:

Whenever a PASSING clause refers to a column of an XMLType table in a query, that table must appear before the XMLTable expression in the query FROM list. This is because the XMLTable expression depends on the XMLType table — a left lateral (correlated) join is needed, to ensure a one-to-many (1:N) relationship between the XMLType table row accessed and the rows generated from it by XMLTable.

Example 18-10 Using XMLQuery with Schema-Based Data

This example is similar to Example 18-9 in its effect. It uses XMLQuery, instead of XMLTable, to query hr.purchaseorder. These two examples differ in their treatment of the empty sequences returned by the XQuery expression. In Example 18-9, these empty sequences are not joined with the purchaseorder table, so the overall SQL-query result set has only ten rows. In Example 18-10, these empty sequences are part of the overall result set of the SQL query, which contains 132 rows, one for each of the rows in table purchaseorder. All but ten of those rows are empty, and show up in the output as empty lines. To save space here, those empty lines have been removed.

SELECT XMLQuery('for $i in /PurchaseOrder
                 where $i/CostCenter eq "A10"
                   and $i/User eq "SMCCAIN"
                 return <A10po pono="{$i/Reference}"/>'
                PASSING OBJECT_VALUE
                RETURNING CONTENT)
  FROM purchaseorder;
 
XMLQUERY('FOR$IIN/PURCHASEORDERWHERE$I/COSTCENTEREQ"A10"AND$I/USEREQ"SMCCAIN"RET
--------------------------------------------------------------------------------
<A10po pono="SMCCAIN-20021009123336151PDT"></A10po>
<A10po pono="SMCCAIN-20021009123336341PDT"></A10po>
<A10po pono="SMCCAIN-20021009123337173PDT"></A10po>
<A10po pono="SMCCAIN-20021009123335681PDT"></A10po>
<A10po pono="SMCCAIN-20021009123335470PDT"></A10po>
<A10po pono="SMCCAIN-20021009123336972PDT"></A10po>
<A10po pono="SMCCAIN-20021009123336842PDT"></A10po>
<A10po pono="SMCCAIN-20021009123336512PDT"></A10po>
<A10po pono="SMCCAIN-2002100912333894PDT"></A10po>
<A10po pono="SMCCAIN-20021009123337403PDT"></A10po>
 
132 rows selected.

See Also:

Example 18-17 for the EXPLAIN PLAN of Example 18-10

Example 18-11 Using XMLTable with PASSING and COLUMNS Clauses

This example uses XMLTable clauses PASSING and COLUMNS. The XQuery expression iterates over top-level PurchaseOrder elements, constructing a PO element for each purchase order with cost center A10. The resulting PO elements are then passed to XMLTable for processing.

Data from the children of PurchaseOrder is used to construct the children of PO, which are Ref, Type, and Name. The content of Type is taken from the content of /PurchaseOrder/SpecialInstructions, but the classes of SpecialInstructions are divided up differently for Type.

Function XMLTable breaks up the result of XQuery evaluation, returning it as three VARCHAR2 columns of a virtual table: poref, priority, and contact. The DEFAULT clause is used to supply a default priority of Regular.

SELECT xtab.poref, xtab.priority, xtab.contact
  FROM purchaseorder,
       XMLTable('for $i in /PurchaseOrder
                 let $spl := $i/SpecialInstructions
                 where $i/CostCenter eq "A10"
                 return <PO>
                          <Ref>{$i/Reference}</Ref>
                          {if ($spl eq "Next Day Air" or $spl eq "Expedite") then
                             <Type>Fastest</Type>
                           else if ($spl eq "Air Mail") then
                             <Type>Fast</Type>
                           else ()}
                          <Name>{$i/Requestor}</Name>
                        </PO>'
                PASSING OBJECT_VALUE
                COLUMNS poref    VARCHAR2(20) PATH 'Ref',
                        priority VARCHAR2(8)  PATH 'Type' DEFAULT 'Regular',
                        contact  VARCHAR2(20) PATH 'Name') xtab;
 
POREF                PRIORITY CONTACT
-------------------- -------- --------------------
SKING-20021009123336 Fastest  Steven A. King
SMCCAIN-200210091233 Regular  Samuel B. McCain
SMCCAIN-200210091233 Fastest  Samuel B. McCain
JCHEN-20021009123337 Fastest  John Z. Chen
JCHEN-20021009123337 Regular  John Z. Chen
SKING-20021009123337 Regular  Steven A. King
SMCCAIN-200210091233 Regular  Samuel B. McCain
JCHEN-20021009123338 Regular  John Z. Chen
SMCCAIN-200210091233 Regular  Samuel B. McCain
SKING-20021009123335 Regular  Steven X. King
SMCCAIN-200210091233 Regular  Samuel B. McCain
SKING-20021009123336 Regular  Steven A. King
SMCCAIN-200210091233 Fast     Samuel B. McCain
SKING-20021009123336 Fastest  Steven A. King
SKING-20021009123336 Fastest  Steven A. King
SMCCAIN-200210091233 Regular  Samuel B. McCain
JCHEN-20021009123335 Regular  John Z. Chen
SKING-20021009123336 Regular  Steven A. King
JCHEN-20021009123336 Regular  John Z. Chen
SKING-20021009123336 Regular  Steven A. King
SMCCAIN-200210091233 Regular  Samuel B. McCain
SKING-20021009123337 Regular  Steven A. King
SKING-20021009123338 Fastest  Steven A. King
SMCCAIN-200210091233 Regular  Samuel B. McCain
JCHEN-20021009123337 Regular  John Z. Chen
JCHEN-20021009123337 Regular  John Z. Chen
JCHEN-20021009123337 Regular  John Z. Chen
SKING-20021009123337 Regular  Steven A. King
JCHEN-20021009123337 Regular  John Z. Chen
SKING-20021009123337 Regular  Steven A. King
SKING-20021009123337 Regular  Steven A. King
SMCCAIN-200210091233 Fast     Samuel B. McCain
 
32 rows selected.

Example 18-12 Using XMLTable to Decompose XML Collection Elements into Relational Data

In this example, SQL function XMLTable is used to break up the XML data in an XMLType collection element, LineItem, into separate columns of a virtual table.

SELECT lines.lineitem, lines.description, lines.partid,
       lines.unitprice, lines.quantity
  FROM purchaseorder,
       XMLTable('for $i in /PurchaseOrder/LineItems/LineItem
                 where $i/@ItemNumber >= 8
                  and $i/Part/@UnitPrice > 50
                  and $i/Part/@Quantity > 2
                 return $i'
                PASSING OBJECT_VALUE
                COLUMNS lineitem    NUMBER       PATH '@ItemNumber',
                        description VARCHAR2(30) PATH 'Description',
                        partid      NUMBER       PATH 'Part/@Id',
                        unitprice   NUMBER       PATH 'Part/@UnitPrice',
                        quantity    NUMBER       PATH 'Part/@Quantity') lines; 

LINEITEM DESCRIPTION                           PARTID UNITPRICE QUANTITY
-------- ------------------------------ ------------- --------- --------
      11 Orphic Trilogy                   37429148327        80        3
      22 Dreyer Box Set                   37429158425        80        4
      11 Dreyer Box Set                   37429158425        80        3
      16 Dreyer Box Set                   37429158425        80        3
       8 Dreyer Box Set                   37429158425        80        3
      12 Brazil                           37429138526        60        3
      18 Eisenstein: The Sound Years      37429149126        80        4
      24 Dreyer Box Set                   37429158425        80        3
      14 Dreyer Box Set                   37429158425        80        4
      10 Brazil                           37429138526        60        3
      17 Eisenstein: The Sound Years      37429149126        80        3
      16 Orphic Trilogy                   37429148327        80        4
      13 Orphic Trilogy                   37429148327        80        4
      10 Brazil                           37429138526        60        4
      12 Eisenstein: The Sound Years      37429149126        80        3
      12 Dreyer Box Set                   37429158425        80        4
      13 Dreyer Box Set                   37429158425        80        4
 
17 rows selected.

See Also:

Using Namespaces with XQuery

You can use the XQuery declare namespace declaration in the prolog of an XQuery expression to define a namespace prefix. You can use declare default namespace to establish the namespace as the default namespace for the expression.

Be aware of the following pitfall, if you use SQL*Plus: If the semicolon (;) at the end of a namespace declaration terminates a line, SQL*Plus will interpret it as a SQL terminator. To avoid this, you can do one of the following:

  • Place the text that follows the semicolon on the same line.

  • Place a comment, such as (: :), after the semicolon, on the same line.

  • Turn off the recognition of the SQL terminator with SQL*Plus command SET SQLTERMINATOR.

Example 18-13 Using XMLQuery with a Namespace Declaration

SELECT XMLQuery('declare namespace e = "http://emp.com";
ERROR:
ORA-01756: quoted string not properly terminated
 
                 for $i in doc("/public/empsns.xml")/e:emps/e:emp
SP2-0734: unknown command beginning "for $i in ..." - rest of line ignored.
...

-- This works - do not end the line with ";".
SELECT XMLQuery('declare namespace e = "http://emp.com"; for
                     $i in doc("/public/empsns.xml")/e:emps/e:emp
                 let $d := 
                   doc("/public/depts.xml")//dept[deptno=$i/@e:deptno]/@dname
                 where $i/@e:salary > 100000
                 order by $i/@e:empno
                 return <emp ename="{$i/@e:ename}" dept="{$d}"/>'
                RETURNING CONTENT) FROM DUAL;
 
XMLQUERY('DECLARENAMESPACEE="HTTP://EMP.COM";FOR$IINDOC("/PUBLIC/EMPSNS.XML")/E:
--------------------------------------------------------------------------------
<emp ename="Jack" dept=""></emp><emp ename="Jill" dept=""></emp>

-- This works too - add a comment after the ";".
SELECT XMLQuery('declare namespace e = "http://emp.com";  (: :)
                 for $i in doc("/public/empsns.xml")/e:emps/e:emp
                 let $d := doc("/public/depts.xml")//dept[deptno=$i/@e:deptno]/@dname
                 where $i/@e:salary > 100000
                 order by $i/@e:empno
                 return <emp ename="{$i/@e:ename}" dept="{$d}"/>'
                RETURNING CONTENT) FROM DUAL;
 
XMLQUERY('DECLARENAMESPACEE="HTTP://EMP.COM";(::)FOR$IINDOC("/PUBLIC/EMPSNS.XML"
--------------------------------------------------------------------------------
<emp ename="Jack" dept=""></emp><emp ename="Jill" dept=""></emp>
 
1 row selected.

-- This works too - tell SQL*Plus to ignore the ";".
SET SQLTERMINATOR OFF
 
SELECT XMLQuery('declare namespace e = "http://emp.com";
                 for $i in doc("/public/empsns.xml")/e:emps/e:emp
                 let $d :=
                   doc("/public/depts.xml")//dept[deptno=$i/@e:deptno]/@dname
                 where $i/@e:salary > 100000
                 order by $i/@e:empno
                 return <emp ename="{$i/@e:ename}" dept="{$d}"/>'
                RETURNING CONTENT) FROM DUAL
/
 
XMLQUERY('DECLARENAMESPACEE="HTTP://EMP.COM";FOR$IINDOC("/PUBLIC/EMPSNS.XML")/E:
--------------------------------------------------------------------------------
<emp ename="Jack" dept=""></emp><emp ename="Jill" dept=""></emp>

An XQuery namespace declaration has no effect outside of its XQuery expression. To declare a namespace prefix for use in an XMLTable expression outside of the XQuery expression, use the XMLNAMESPACES clause. This clause also covers the XQuery expression argument to XMLTable, eliminating the need for a separate declaration in the XQuery prolog.

In Example 18-14, XMLNAMESPACES is used to define the prefix e for the namespace http://emp.com. This namespace is used in the COLUMNS clause as well as the XQuery expression of the XMLTable expression.

Example 18-14 Using XMLTable with the XMLNAMESPACES Clause

SELECT * FROM XMLTable(XMLNAMESPACES('http://emp.com' AS "e"),
                       'for $i in doc("/public/empsns.xml")
                        return $i/e:emps/e:emp'
                       COLUMNS name VARCHAR2(6) PATH '@ename',
                               id   NUMBER      PATH '@empno');

This produces the following result:

NAME           ID
------ ----------
John            1
Jack            2
Jill            3
 
3 rows selected.

It is the presence of qualified names e:ename and e:empno in the COLUMNS clause that necessitates using the XMLNAMESPACES clause. Otherwise, a prolog namespace declaration (declare namespace e = "http://emp.com") would suffice for the XQuery expression itself.

Because the same namespace is used throughout the XMLTable expression, a default namespace could be used: XMLNAMESPACES (DEFAULT 'http://emp.com'). The qualified name $i/e:emps/e:emp could then be written without an explicit prefix: $i/emps/emp.

Performance Tuning for XQuery

As mentioned, Oracle XML DB generally evaluates XQuery expressions by executing equivalent relational expressions. This optimization uses the same mechanism as XPath rewrite, and it provides the same benefits. Just as query tuning can improve SQL performance, so it can improve XQuery performance. You tune XQuery performance by choosing appropriate XML storage models and indexes.

As with database queries generally, you determine whether tuning is required by examining the EXPLAIN PLAN for a query. If the plan is not optimal, then consult the following documentation for specific tuning information:

In addition, be aware that the following XQuery expressions can be expensive to process, so they might add performance overhead when processing large volumes of data:

This section presents the EXPLAIN PLANs for some of the examples shown earlier in this chapter, to indicate how they are executed. The examples are organized into the following groups according to the target of the XQuery expression:

To further improve the performance of XQuery expressions when querying XMLType data in unstructured storage or binary XML storage, you can use XMLIndex.

XQuery Optimization over a SQL/XML View Created by ora:view

Example 18-15 shows the optimization of XMLQuery over a SQL/XML view created by ora:view. Example 18-16 shows the optimization of XMLTable in the same context.

Example 18-15 Optimization of XMLQuery with ora:view

Here, again, is Example 18-6:

SELECT XMLQuery(
         'for $i in ora:view("OE", "WAREHOUSES")/ROW
          return <Warehouse id="{$i/WAREHOUSE_ID}">
                 <Location>
                   {for $j in ora:view("HR", "LOCATIONS")/ROW 
                    where $j/LOCATION_ID eq $i/LOCATION_ID 
                    return ($j/STREET_ADDRESS, $j/CITY, $j/STATE_PROVINCE)}
                 </Location>    
                 </Warehouse>'
         RETURNING CONTENT) FROM DUAL;

The EXPLAIN PLAN for this example shows that the query has been optimized:

PLAN_TABLE_OUTPUT
--------------------------------------------------------------------------------------------
Plan hash value: 2976528487
 
--------------------------------------------------------------------------------------------
| Id  | Operation                     | Name       | Rows  | Bytes | Cost (%CPU)| Time     |
--------------------------------------------------------------------------------------------
|   0 | SELECT STATEMENT              |            |     1 |       |     2   (0)| 00:00:01 |
|   1 |  SORT AGGREGATE               |            |     1 |    41 |            |          |
|   2 |   NESTED LOOPS                |            |     1 |    41 |     3   (0)| 00:00:01 |
|   3 |    TABLE ACCESS BY INDEX ROWID| LOCATIONS  |     1 |    41 |     1   (0)| 00:00:01 |
|*  4 |     INDEX UNIQUE SCAN         | LOC_ID_PK  |     1 |       |     0   (0)| 00:00:01 |
|   5 |    FAST DUAL                  |            |     1 |       |     2   (0)| 00:00:01 |
|   6 |     SORT AGGREGATE            |            |     1 |   185 |            |          |
|   7 |      NESTED LOOPS             |            |     9 |  1665 |     4   (0)| 00:00:01 |
|   8 |       FAST DUAL               |            |     1 |       |     2   (0)| 00:00:01 |
|   9 |       TABLE ACCESS FULL       | WAREHOUSES |     9 |  1665 |     2   (0)| 00:00:01 |
|  10 |        FAST DUAL              |            |     1 |       |     2   (0)| 00:00:01 |
--------------------------------------------------------------------------------------------
 
Predicate Information (identified by operation id):
---------------------------------------------------
 
 4 - access("LOCATION_ID"=:B1)
 
22 rows selected.

Example 18-16 Optimization of XMLTable with ora:view

Here, again, is Example 18-7:

SELECT * 
  FROM XMLTable(
         'for $i in ora:view("OE", "WAREHOUSES")/ROW
          return <Warehouse id="{$i/WAREHOUSE_ID}">
                   <Location>
                     {for $j in ora:view("HR", "LOCATIONS")/ROW
                      where $j/LOCATION_ID eq $i/LOCATION_ID 
                      return ($j/STREET_ADDRESS, $j/CITY, $j/STATE_PROVINCE)} 
                   </Location>
                 </Warehouse>');

The EXPLAIN PLAN for this example shows that the query has been optimized:

PLAN_TABLE_OUTPUT
--------------------------------------------------------------------------------------------
Plan hash value: 2573750906
 
--------------------------------------------------------------------------------------------
| Id  | Operation                     | Name       | Rows  | Bytes | Cost (%CPU)| Time     |
--------------------------------------------------------------------------------------------
|   0 | SELECT STATEMENT              |            |     9 |  1665 |     4   (0)| 00:00:01 |
|   1 |  SORT AGGREGATE               |            |     1 |    41 |            |          |
|   2 |   NESTED LOOPS                |            |     1 |    41 |     3   (0)| 00:00:01 |
|   3 |    TABLE ACCESS BY INDEX ROWID| LOCATIONS  |     1 |    41 |     1   (0)| 00:00:01 |
|*  4 |     INDEX UNIQUE SCAN         | LOC_ID_PK  |     1 |       |     0   (0)| 00:00:01 |
|   5 |    FAST DUAL                  |            |     1 |       |     2   (0)| 00:00:01 |
|   6 |     NESTED LOOPS              |            |     9 |  1665 |     4   (0)| 00:00:01 |
|   7 |      FAST DUAL                |            |     1 |       |     2   (0)| 00:00:01 |
|   8 |      TABLE ACCESS FULL        | WAREHOUSES |     9 |  1665 |     2   (0)| 00:00:01 |
--------------------------------------------------------------------------------------------
 
Predicate Information (identified by operation id):
---------------------------------------------------
 
   4 - access("LOCATION_ID"=:B1)
 
20 rows selected.

XQuery Optimization over XML Schema-Based XMLType Data

Example 18-17 shows the optimization of XMLQuery over an XML schema-based XMLType table. Example 18-18 shows the optimization of XMLTable in the same context.

Example 18-17 Optimization of XMLQuery with Schema-Based XMLType Data

Here, again, is Example 18-10:

SELECT XMLQuery('for $i in /PurchaseOrder
                 where $i/CostCenter eq "A10"
                   and $i/User eq "SMCCAIN"
                 return <A10po pono="{$i/Reference}"/>'
                PASSING OBJECT_VALUE
                RETURNING CONTENT)
  FROM purchaseorder;
 

The EXPLAIN PLAN for this example shows that the query has been optimized.

PLAN_TABLE_OUTPUT
-------------------------------------------------------------------------------------
Plan hash value: 3611789148
 
-------------------------------------------------------------------------------------
| Id  | Operation           | Name          | Rows  | Bytes | Cost (%CPU)| Time     |
-------------------------------------------------------------------------------------
|   0 | SELECT STATEMENT    |               |     1 |   530 |     5   (0)| 00:00:01 |
|   1 |  SORT AGGREGATE     |               |     1 |       |            |          |
|*  2 |   FILTER            |               |       |       |            |          |
|   3 |    FAST DUAL        |               |     1 |       |     2   (0)| 00:00:01 |
|*  4 |    TABLE ACCESS FULL| PURCHASEORDER |     1 |   530 |     5   (0)| 00:00:01 |
-------------------------------------------------------------------------------------
 
Predicate Information (identified by operation id):
---------------------------------------------------
 
   2 - filter(:B1='SMCCAIN' AND :B2='A10')
   4 - filter(SYS_CHECKACL("ACLOID","OWNERID",xmltype('<privilege
              xmlns="http://xmlns.oracle.com/xdb/acl.xsd"
              xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
              xsi:schemaLocation="http://xmlns.oracle.com/xdb/acl.xsd
              http://xmlns.oracle.com/xdb/acl.xsd DAV:http://xmlns.oracle.com/xdb/dav.xsd">
              <read-properties/><read-contents/></privilege>'))=1)
 
22 rows selected.

Example 18-18 Optimization of XMLTable with Schema-Based XMLType Data

Here, again, is Example 18-12:

SELECT lines.lineitem, lines.description, lines.partid,
       lines.unitprice, lines.quantity
  FROM purchaseorder,
       XMLTable('for $i in /PurchaseOrder/LineItems/LineItem
                 where $i/@ItemNumber >= 8
                  and $i/Part/@UnitPrice > 50
                  and $i/Part/@Quantity > 2
                 return $i'
                PASSING OBJECT_VALUE
                COLUMNS lineitem    NUMBER       PATH '@ItemNumber',
                        description VARCHAR2(30) PATH 'Description',
                        partid      NUMBER       PATH 'Part/@Id',
                        unitprice   NUMBER       PATH 'Part/@UnitPrice',
                        quantity    NUMBER       PATH 'Part/@Quantity') lines;
 

The EXPLAIN PLAN for this example shows that the query has been optimized. The XQuery result is never materialized. Instead, the underlying storage columns for the XML collection element LineItem are used to generate the overall result set.

PLAN_TABLE_OUTPUT
----------------------------------------------------------------------------------------
Plan hash value: 3113556559

----------------------------------------------------------------------------------------
| Id  | Operation          | Name              | Rows  | Bytes | Cost (%CPU)| Time     |
----------------------------------------------------------------------------------------
|   0 | SELECT STATEMENT   |                   |     4 |   376 |     6   (0)| 00:00:01 |
|   1 |  NESTED LOOPS      |                   |     4 |   376 |     6   (0)| 00:00:01 |
|*  2 |   TABLE ACCESS FULL| PURCHASEORDER     |     1 |    37 |     5   (0)| 00:00:01 |
|*  3 |   INDEX RANGE SCAN | SYS_IOT_TOP_48748 |     3 |   171 |     1   (0)| 00:00:01 |
----------------------------------------------------------------------------------------

Predicate Information (identified by operation id):
---------------------------------------------------
 
   2 - filter(SYS_CHECKACL("ACLOID","OWNERID",xmltype('<privilege
              xmlns="http://xmlns.oracle.com/xdb/acl.xsd"
              xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
              xsi:schemaLocation="http://xmlns.oracle.com/xdb/acl.xsd
              http://xmlns.oracle.com/xdb/acl.xsd DAV:http://xmlns.oracle.com/xdb/dav.xsd"><re
              ad-properties/><read-contents/></privilege>'))=1)
   3 - access("NESTED_TABLE_ID"="PURCHASEORDER"."SYS_NC0003400035$")
       filter("SYS_NC00013$">50 AND "SYS_NC00012$">2 AND "ITEMNUMBER">=8)
 
22 rows selected.

In this example, table hr.purchaseorder is traversed completely; the XMLTable expression is evaluated for each purchase-order document. It is more efficient, however, to have the XMLTable expression, not the purchaseorder table, drive the SQL-query execution. That is, although the XQuery expression has been rewritten to relational expressions, you can improve this optimization by creating an index on the underlying relational data — you can optimize this query in the same way that you would optimize a purely SQL query.

That is always the case with XQuery in Oracle XML DB: the optimization techniques you use are the same that you use in SQL.

The UnitPrice attribute of collection element LineItem is an appropriate index target. The governing XML schema specifies that an ordered collection table (OCT) is used to store the LineItem elements.

However, the name of this OCT was generated by Oracle XML DB when the XML purchase-order documents were decomposed as XML schema-based data. Instead of using table purchaseorder from sample database-schema hr, for illustration we will manually create a new purchaseorder table (in a different database schema) with the same properties and same data, but having OCTs with user-friendly names. Refer to Example 3-11 for how to do this.

Assuming that a purchaseorder table has been created as in Example 3-11, the following statement creates the appropriate index:

CREATE INDEX unitprice_index ON lineitem_table("PART"."UNITPRICE");

With this index defined, Example 18-12 results in the following EXPLAIN PLAN, which shows that the XMLTable expression has driven the overall evaluation.

PLAN_TABLE_OUTPUT
----------------------------------------------------------------------------------------
Plan hash value: 1578014525
 
----------------------------------------------------------------------------------------
| Id  | Operation          | Name              | Rows  | Bytes | Cost (%CPU)| Time     |
----------------------------------------------------------------------------------------
|   0 | SELECT STATEMENT   |                   |     3 |   624 |     8   (0)| 00:00:01 |
|   1 |  NESTED LOOPS      |                   |     3 |   624 |     8   (0)| 00:00:01 |
|*  2 |   INDEX UNIQUE SCAN| SYS_IOT_TOP_49323 |     3 |   564 |     5   (0)| 00:00:01 |
|*  3 |    INDEX RANGE SCAN| UNITPRICE_INDEX   |    20 |       |     2   (0)| 00:00:01 |
|*  4 |   INDEX UNIQUE SCAN| SYS_C004411       |     1 |       |     0   (0)| 00:00:01 |
----------------------------------------------------------------------------------------
 
Predicate Information (identified by operation id):
---------------------------------------------------
 
   2 - access("SYS_NC00013$">50)
       filter("ITEMNUMBER">=8 AND "SYS_NC00012$">2)
   3 - access("SYS_NC00013$">50)
   4 - access("NESTED_TABLE_ID"="PURCHASEORDER"."SYS_NC0003400035$")
 
Note
-----
   - dynamic sampling used for this statement
 
23 rows selected.

XQuery Static Type-Checking in Oracle XML DB

Oracle XML DB type-checks all XQuery expressions. Doing this at runtime can be costly, however. As an optimization technique, whenever there is sufficient static type information available for a given query at compile time, Oracle XML DB performs static (compile time) type-checking of that query. Whenever sufficient static type information is not available for a given query at compile time, Oracle XML DB uses dynamic (runtime) type checking for that query.

Static type-checking can save execution time by raising errors at compile time. Static type-checking errors include both data-type errors and the use of XPath expressions that are invalid with respect to an XML schema.

Typical ways of providing sufficient static type information at query compile time include the following:

This section presents examples that demonstrate the utility of static type-checking and the use of these two means of communicating type information.

Example 18-19 Static Type-Checking of XQuery Expressions: ora:view

The XML view produced on the fly by Oracle XQuery function ora:view has ROW as its top-level element, but this example incorrectly lacks that ROW wrapper element. This omission raises a compile-time error. Forgetting that ora:view wraps relational data in this way is an easy mistake to make, and one that could be difficult to diagnose without static type-checking. Example 18-5 shows the correct code.

-- This produces a static-type-check error, because "ROW" is missing.
SELECT XMLQuery('for $i in ora:view("REGIONS"), $j in ora:view("COUNTRIES")
                 where $i/REGION_ID = $j/REGION_ID and $i/REGION_NAME = "Asia"
                 return $j'
                RETURNING CONTENT) AS asian_countries
  FROM DUAL;
SELECT XMLQuery('for $i in ora:view("REGIONS"), $j in ora:view("COUNTRIES")
*
ERROR at line 1:
ORA-19276: XPST0005 - XPath step specifies an invalid element/attribute name:
(REGION_ID)

Example 18-20 Static Type-Checking of XQuery Expressions: Schema-Based XML

In this example, XQuery static type-checking finds a mismatch between an XPath expression and its target XML schema-based data. Element CostCenter is misspelled here as costcenter (XQuery and XPath are case-sensitive). Example 18-11 shows the correct code.

-- This results in a static-type-check error: CostCenter is not the right case.
SELECT xtab.poref, xtab.usr, xtab.requestor
  FROM purchaseorder,
       XMLTable('for $i in /PurchaseOrder where $i/costcenter eq "A10" return $i'
                PASSING OBJECT_VALUE
                COLUMNS poref     VARCHAR2(20) PATH 'Reference',
                        usr       VARCHAR2(20) PATH 'User' DEFAULT 'Unknown',
                        requestor VARCHAR2(20) PATH 'Requestor') xtab;
  FROM purchaseorder,
       *
ERROR at line 2:
ORA-19276: XPST0005 - XPath step specifies an invalid element/attribute name:
(costcenter)

SQL*Plus XQUERY Command

Example 18-21 shows how you can enter an XQuery expression directly at the SQL*Plus command line, by preceding the expression with the SQL*Plus command XQUERY and following it with a slash (/) on a line by itself. Oracle Database treats XQuery expressions submitted with this command the same way it treats XQuery expressions in SQL functions XMLQuery and XMLTable. Execution is identical, with the same optimizations.

Example 18-21 Using the SQL*Plus XQUERY Command

SQL> XQUERY for $i in ora:view("departments")
  2  where $i/ROW/DEPARTMENT_ID < 50
  3  return $i
  4  /
 
Result Sequence
--------------------------------------------------------------------------------
<ROW><DEPARTMENT_ID>10</DEPARTMENT_ID><DEPARTMENT_NAME>Administration</DEPARTMEN
T_NAME><MANAGER_ID>200</MANAGER_ID><LOCATION_ID>1700</LOCATION_ID></ROW>
 
<ROW><DEPARTMENT_ID>20</DEPARTMENT_ID><DEPARTMENT_NAME>Marketing</DEPARTMENT_NAM
E><MANAGER_ID>201</MANAGER_ID><LOCATION_ID>1800</LOCATION_ID></ROW>
 
<ROW><DEPARTMENT_ID>30</DEPARTMENT_ID><DEPARTMENT_NAME>Purchasing</DEPARTMENT_NA
ME><MANAGER_ID>114</MANAGER_ID><LOCATION_ID>1700</LOCATION_ID></ROW>
 
<ROW><DEPARTMENT_ID>40</DEPARTMENT_ID><DEPARTMENT_NAME>Human Resources</DEPARTME
NT_NAME><MANAGER_ID>203</MANAGER_ID><LOCATION_ID>2400</LOCATION_ID></ROW>

There are also a few SQL*Plus SET commands that you can use for settings that are specific to XQuery. Use SHOW XQUERY to see the current settings.

Using XQuery with PL/SQL, JDBC, and ODP.NET

Previous sections in this chapter have shown how to invoke XQuery from SQL. This section provides examples of using XQuery with the Oracle APIs for PL/SQL, JDBC, and Oracle Data Provider for .NET (ODP.NET).

Example 18-22 Using XQuery with PL/SQL

This example shows how to use XQuery with PL/SQL, in particular, how to bind dynamic variables to an XQuery expression using the XMLQuery PASSING clause. The bind variables :1 and :2 are bound to the PL/SQL bind arguments nbitems and partid, respectively. These are then passed to XQuery as XQuery variables itemno and id, respectively.

DECLARE
  sql_stmt VARCHAR2(2000); -- Dynamic SQL statement to execute
  nbitems  NUMBER := 3; -- Number of items
  partid   VARCHAR2(20):= '715515009058'; -- Part ID
  result   XMLType;
  doc      DBMS_XMLDOM.DOMDocument;
  ndoc     DBMS_XMLDOM.DOMNode;
  buf      VARCHAR2(20000);
BEGIN
  sql_stmt :=
    'SELECT XMLQuery(
              ''for $i in ora:view("PURCHASEORDER") ' ||
               'where count($i/PurchaseOrder/LineItems/LineItem) = $itemno ' ||
                 'and $i/PurchaseOrder/LineItems/LineItem/Part/@Id = $id ' ||
               'return $i/PurchaseOrder/LineItems'' ' ||
              'PASSING :1 AS "itemno", :2 AS "id" ' ||
              'RETURNING CONTENT) FROM DUAL';
 
  EXECUTE IMMEDIATE sql_stmt INTO result USING nbitems, partid;
  doc  := DBMS_XMLDOM.newDOMDocument(result);
  ndoc := DBMS_XMLDOM.makeNode(doc);
  DBMS_XMLDOM.writeToBuffer(ndoc, buf);
  DBMS_OUTPUT.put_line(buf);
END;
/

This produces the following output:

<LineItems>
  <LineItem ItemNumber="1">
    <Description>Samurai 2: Duel at Ichijoji Temple</Description>
    <Part Id="37429125526" UnitPrice="29.95" Quantity="3"/>
  </LineItem>
  <LineItem ItemNumber="2">
    <Description>The Red Shoes</Description>
    <Part Id="37429128220" UnitPrice="39.95" Quantity="4"/>
  </LineItem>
  <LineItem ItemNumber="3">
    <Description>A Night to Remember</Description>
    <Part Id="715515009058" UnitPrice="39.95" Quantity="1"/>
  </LineItem>
</LineItems>
<LineItems>
  <LineItem ItemNumber="1">
    <Description>A Night to Remember</Description>
    <Part Id="715515009058" UnitPrice="39.95" Quantity="2"/>
  </LineItem>
  <LineItem ItemNumber="2">
    <Description>The Unbearable Lightness Of Being</Description>
    <Part Id="37429140222" UnitPrice="29.95" Quantity="2"/>
  </LineItem>
  <LineItem ItemNumber="3">
    <Description>Sisters</Description>
    <Part Id="715515011020" UnitPrice="29.95" Quantity="4"/>
  </LineItem>
</LineItems>

PL/SQL procedure successfully completed.

Example 18-23 Using XQuery with JDBC

This example shows how to use XQuery with JDBC, binding variables by position with the PASSING clause of SQL function XMLTable.

import java.sql.*;
import oracle.sql.*;
import oracle.jdbc.*;
import oracle.xdb.XMLType; 
import java.util.*;
 
public class QueryBindByPos
{
  public static void main(String[] args) throws Exception, SQLException
  {
    System.out.println("*** JDBC Access of XQuery using Bind Variables ***");
    DriverManager.registerDriver(new oracle.jdbc.driver.OracleDriver());
    OracleConnection conn
      = (OracleConnection)
        DriverManager.getConnection("jdbc:oracle:oci8:@localhost:1521:ora11gR1", "oe", "oe");
    String xqString
      = "SELECT COLUMN_VALUE" +
          "FROM XMLTable('for $i in ora:view(\"PURCHASEORDER\") " +
                         "where $i/PurchaseOrder/Reference= $ref " +
                         "return $i/PurchaseOrder/LineItems' " +
                        "PASSING ? AS \"ref\")";
    OraclePreparedStatement stmt = (OraclePreparedStatement)conn.prepareStatement(xqString);
    String refString = "EABEL-20021009123336251PDT"; // Set the filter value
    stmt.setString(1, refString); // Bind the string
    ResultSet rs = stmt.executeQuery();
    while (rs.next())
    {
       XMLType desc = (XMLType) rs.getObject(1);
       System.out.println("LineItem Description: " + desc.getStringVal()); 
    }
    rs.close();
    stmt.close();
  }
}

This produces the following output:

*** JDBC Access of Database XQuery with Bind Variables ***
LineItem Description: Samurai 2: Duel at Ichijoji Temple
LineItem Description: The Red Shoes
LineItem Description: A Night to Remember

Example 18-24 Using XQuery with ODP.NET and C#

This example shows how to use XQuery with ODP.NET and the C# language. The C# input parameters :nbitems and :partid are passed to XQuery as XQuery variables itemno and id, respectively.

using System;
using System.Data;
using System.Text;
using System.IO;
using System.Xml;
using Oracle.DataAccess.Client;
using Oracle.DataAccess.Types;
 
namespace XQuery
{
  /// <summary>
  /// Demonstrates how to bind variables for XQuery calls
  /// </summary>
  class XQuery
  {
    /// <summary>
    /// The main entry point for the application.
    /// </summary>
    static void Main(string[] args)
    {
      int rows = 0;
      StreamReader sr = null;
 
      // Create the connection.
      string constr = "User Id=oe;Password=***********;Data Source=ora11gr1"; // Replace with real password.
      OracleConnection con = new OracleConnection(constr);
      con.Open();
 
      // Create the command.
      OracleCommand cmd = new OracleCommand("", con);
 
      // Set the XML command type to query.
      cmd.CommandType   = CommandType.Text;
        
      // Create the SQL query with the XQuery expression.
      StringBuilder blr = new StringBuilder();
      blr.Append("SELECT column_value FROM XMLTable");
      blr.Append("(\'for $i in ora:view(\"PURCHASEORDER\") ");
      blr.Append("   where count($i/PurchaseOrder/LineItems/LineItem) = $itemno ");
      blr.Append("      and $i/PurchaseOrder/LineItems/LineItem/Part/@Id = $id ");
      blr.Append("   return $i/PurchaseOrder/LineItems\' ");
      blr.Append("  PASSING :nbitems AS \"itemno\", :partid AS \"id\")");
 
      cmd.CommandText = blr.ToString();
      cmd.Parameters.Add(":nbitems", OracleDbType.Int16, 3, ParameterDirection.Input);
      cmd.Parameters.Add(":partid", OracleDbType.Varchar2, "715515009058", ParameterDirection.Input);
 
      // Get the XML document as an XmlReader.
      OracleDataReader dr = cmd.ExecuteReader();
      dr.Read();
 
      // Get the XMLType column as an OracleXmlType
      OracleXmlType xml = dr.GetOracleXmlType(0);
 
      // Print the XML data in the OracleXmlType object
      Console.WriteLine(xml.Value);
      xml.Dispose();
 
      // Clean up.
      cmd.Dispose();
      con.Close();
      con.Dispose();
    }
  }
}

This produces the following output:

<LineItems>
  <LineItem ItemNumber="1">
    <Description>Samurai 2: Duel at Ichijoji Temple</Description>
    <Part Id="37429125526" UnitPrice="29.95" Quantity="3"/>
  </LineItem>
  <LineItem ItemNumber="2">
    <Description>The Red Shoes</Description>
    <Part Id="37429128220" UnitPrice="39.95" Quantity="4"/>
  </LineItem>
  <LineItem ItemNumber="3">
    <Description>A Night to Remember</Description>
    <Part Id="715515009058" UnitPrice="39.95" Quantity="1"/>
  </LineItem>
</LineItems>

Oracle XML DB Support for XQuery

This section describes Oracle XML DB for the XQuery language.

Support for XQuery and SQL

Support for the XQuery language in Oracle XML DB is designed to provide the best fit between the worlds of relational storage and querying XML data. That is, Oracle XML DB is a general XQuery implementation, but it is in addition specifically designed to make relational and XQuery queries work well together.

The specific properties of the Oracle XML DB XQuery implementation are described in this section. The XQuery standard explicitly calls out certain aspects of the language processing as implementation-defined or implementation-dependent. There are also some features that are specified by the XQuery standard but are not supported by Oracle XML DB.

Implementation Choices Specified in the XQuery Standard

The XQuery specification specifies that each of the following aspects of language processing is to be defined by the implementation.

  • Implicit time zone support – In Oracle XML DB, the implicit time zone is always assumed to be Z, and instances of xs:date, xs:time, and xs:datetime that are missing time zones are  automatically converted to UTC.

XQuery Features Not Supported by Oracle XML DB

The following features specified by the XQuery standard are not supported by Oracle XML DB:

  • Copy-namespace mode – Oracle XML DB supports only preserve and inherit for a copy-namespaces declaration. This means that when an existing element node is copied by an element constructor or document constructor, all in-scope namespaces of the original element are retained in the copy, and, otherwise, the copied node inherits all in-scope namespaces of the constructed node. An error is raised if you specify no-preserve or no-inherit.

  • Version encoding – Oracle XML DB does not support an optional encoding declaration in a version declaration. That is, you cannot include (encoding an-encoding) in a declaration xquery version a-version;. This means that you cannot specify an encoding used in the query. An error is raised if you include an encoding declaration.

  • xml:id – Oracle XML DB does not support use of xml:id. If you use xml:id, then an error is raised.

  • XQuery prolog default-collation declaration.

  • XQuery prolog boundary-space declaration.

  • XQuery data type xs:duration. Use either xs:yearMonthDuration or xs:DayTimeDuration instead.

XQuery Optional Features

The following optional features specified by the XQuery standard are not supported by Oracle XML DB:

  • Schema Validation Feature

  • Module Feature

In addition to these defined optional features, the W3C specification lets an implementation provide implementation-defined pragmas and extensions. These include the following:

  • Pragmas

  • Must-understand extensions

The Oracle implementation does not require any such pragmas or extensions.

Support for XQuery Functions and Operators

Oracle XML DB supports all of the XQuery functions and operators included in the latest XQuery 1.0 and XPath 2.0 Functions and Operators specification, with the following exceptions. There is no support for the following:

  • The XQuery regular-expression functions: fn:matches, fn:replace, and fn:tokenizer. Use Oracle XQuery functions ora:matches and ora:replace instead of fn:matches and fn:replace.

  • Functions fn:id and fn:idref.

  • Function fn:collection without arguments.

  • Optional collation parameters for XQuery functions.

XQuery Functions fn:doc, fn:collection, and fn:doc-available

Oracle XML DB supports the XQuery functions fn:doc, fn:collection, and fn:doc-available for all resources in Oracle XML DB Repository.

Function doc returns the repository file resource that is targeted by its URI argument; it must be a file of well-formed XML data. Function collection is similar, but works on repository folder resources (each file in the folder must contain well-formed XML data). Each of these functions returns an empty sequence if the targeted resource is not found – it does not raise an error. Function fn:doc-available tests whether its resource argument exists; it returns true if so, false if not.

See Also:

http://www.w3.org for the definitions of XQuery functions and operators


Footnote Legend

Footnote 1: The value returned is a sequence, as always. However, in XQuery, a sequence of one item is equivalent to that item itself. In this case, the single item is a Boolean value.
Footnote 2: Namespace prefix xs is predefined for the XML Schema namespace, http://www.w3.org/2001/XMLSchema.
Footnote 3: The question mark (?) here is a zero-or-one occurrence indicator that indicates that the argument can be the empty sequence. See "XQuery Expressions".
Footnote 4: The question mark (?) here is a zero-or-one occurrence indicator that indicates that the argument can be the empty sequence. See "XQuery Expressions".
Footnote 5: The asterisk (*) here is a zero-or-more occurrence indicator that indicates that the argument can be a possibly empty sequence of document nodes of type element. See "XQuery Expressions".