XMLQUERY

Syntax

XML_passing_clause::=

Purpose

XMLQUERY lets you query XML data in SQL statements. It takes an XQuery expression as a string literal, an optional context item, and other bind variables and returns the result of evaluating the XQuery expression using these input values.

• XQuery_string is a complete XQuery expression, including prolog.

• The expr in the XML_passing_clause is an expression returning an XMLType or an instance of a SQL scalar data type that is used as the context for evaluating the XQuery expression. You can specify only one expr in the PASSING clause without an identifier. The result of evaluating each expr is bound to the corresponding identifier in the XQuery_string. If any expr that is not followed by an AS clause, then the result of evaluating that expression is used as the context item for evaluating the XQuery_string.

• RETURNING CONTENT indicates that the result from the XQuery evaluation is either an XML 1.0 document or a document fragment conforming to the XML 1.0 semantics.

• If the result set is empty, then the function returns the SQL NULL value. The NULL ON EMPTY keywords are implemented by default and are shown for semantic clarity.

Examples

The following statement specifies the warehouse_spec column of the oe.warehouses table in the XML_passing_clause as a context item. The statement returns specific information about the warehouses with area greater than 50K.

SELECT warehouse_name,
EXTRACTVALUE(warehouse_spec, '/Warehouse/Area'),
XMLQuery(
   'for $i in /Warehouse
   where $i/Area > 50000
   return <Details>
             <Docks num="{$i/Docks}"/>
             <Rail>
               {
               if ($i/RailAccess = "Y") then "true" else "false"
               }
             </Rail>
          </Details>' PASSING warehouse_spec RETURNING CONTENT) "Big_warehouses"
   FROM warehouses;

WAREHOUSE_ID Area      Big_warehouses
------------ --------- --------------------------------------------------------
           1     25000
           2     50000
           3     85700 <Details><Docks></Docks><Rail>false</Rail></Details>
           4    103000 <Details><Docks num="3"></Docks><Rail>true</Rail></Details>
 . . .