XQuery prologs and expressions

In XQuery, an XQuery expression consists of an optional prolog that is followed by an expression. The prolog contains a series of declarations that define the processing environment for the expression. The path expression consists of an expression that defines the result of the XQuery expression.

Syntax

The following diagrams show the general format of an XQuery expression.


XQuery expression

>>-+--------+--expression--------------------------------------><
   '-prolog-'


expression

|--+-primary-expression----+------------------------------------|
   +-logical-expression----+   
   +-comparison-expression-+   
   +-arithmetic-expression-+   
   '-path-expression-------'


prolog

   .-----------------------------------.   
   V                                   |   
|----+-boundary-space-declaration----+-+------------------------|
     +-copy-namespaces-declaration---+     
     +-namespace-declaration---------+     
     '-default-namespace-declaration-'

Example

The following example illustrates the structure of a typical expression in XQuery. In this example, the prolog contains a namespace declaration that binds the prefix ns1 to a URI. The expression body contains an expression that returns all documents in the XMLPO column where the name attribute on the shipTo node is "Jane" and the name attribute on the billTo node is "Jason":

Figure 1. Structure of a typical expression in XQuery

SELECT XMLQUERY ('declare namespace ipo="http://www.example.com/IPO";
/ipo:purchaseOrder[shipTo/name = "Jane" and
billTo/name = "Jason"]'
PASSING XMLPO)
FROM T1;