XML Instance Oracle Tips by Laurent Schneider

 

Laurent Schneider is considered one of the top Oracle SQL experts, and he is the author of the book "Advanced SQL Programming" by Rampant TechPress.  The following is an excerpt from the book.

 

XML

XML functionality is part of the Oracle Database.  

XML Instance

An instance could be a well-formed XML document. An XML document contains a root node:

<DOC>
   <ELEM id="1"/>
   <ELEM id="2"/>
</DOC> 

An instance could be well-formed XML content. XML content does not require a root node:

<ELEM>1</ELEM>
<ELEM>2</ELEM>

An XML instance could also contains simple data:

1000

XMLTYPE

XMLTYPEis the datatype used to store XML data. The type constructor accepts different input like character, binary or ref cursor. The text passed to the constructor must be a well-formed document. 

SELECT
   XMLTYPE
   (
      '<X/>'
   )
FROM
   DUAL; 

XMLTYPE
-------
<X/>

The XMLTYPE is constructed from a character literal.

SELECT
   XMLTYPE
   (
      TO_BLOB
      (
         HEXTORAW ('3C696D673E3A2D293C2F696D673E')
      ),
      NLS_CHARSET_ID('WE8MSWIN1252')
   )
FROM
   DUAL;

XMLTYPE(TO_BLOB
---------------
<img>:-)</img>

A BLOBis passed to the XMLTYPE constructor.

NLS_CHARSET_IDreturns the character set used for the encoding of the BLOB. Oracle 9i does not support BLOB as input.

SELECT
   XMLTYPE
   (
      BFILENAME('TEMP', 'test.xml'),
      NLS_CHARSET_ID('WE8MSWIN1252')
   )
FROM
   DUAL;

XMLTYPE(BFILENAME('TEM
----------------------
<msg>Hello World</msg>

A file is passed to the XMLTYPE constructor. BFILENAME returns a BFILElocator to the file test.xml in the Oracle directory TEMP.

SELECT
   XMLTYPE
   (
      CURSOR
      (           
         SELECT
            *
         FROM
            DEPT
      )
   )
FROM
   DUAL;

XMLTYPE(CURSOR(SELECT*FROMDEPT))
--------------------------------
<?xml version="1.0"?>
<ROWSET>
 <ROW>
  <DEPTNO>10</DEPTNO>
  <DNAME>ACCOUNTING</DNAME>
  <LOC>NEW YORK</LOC>
 </ROW>
 <ROW>
  <DEPTNO>20</DEPTNO>
  <DNAME>RESEARCH</DNAME>
  <LOC>DALLAS</LOC>
 </ROW>
 <ROW>
  <DEPTNO>30</DEPTNO>
  <DNAME>SALES</DNAME>
  <LOC>CHICAGO</LOC>
 </ROW>
 <ROW>
  <DEPTNO>40</DEPTNO>
  <DNAME>OPERATIONS</DNAME>
  <LOC>BOSTON</LOC>
 </ROW>
</ROWSET>

XMLTYPE accepts a Ref Cursor as a parameter.

XMLELEMENT

XMLELEMENTis a function that returns an XMLTYPE. The first argument is the name of the tag. The following argument is the value and could be string, XMLTYPE, number, or date.

SELECT
   EMPNO,
   XMLELEMENT(NAME, ENAME) NAME
FROM
   EMP
WHERE
   ENAME LIKE 'S%';
     EMPNO NAME
---------- ------------------------------
      7369 <NAME>SMITH</NAME>
      7788 <NAME>SCOTT</NAME>

XMLELEMENT generates an XML type with a tag NAME and the employee name as value.

XMLELEMENT can be nested and can contain attributes:

SELECT
   EMPNO,
   XMLELEMENT
   (
      EMP,
      XMLATTRIBUTES
      (
         EMPNO,
         DEPTNO
      ),
      XMLELEMENT
      (
         NAME,
         ENAME
      ),
      XMLELEMENT
      (
         JOB,
         JOB
      )
   ) EMP
FROM
   EMP
WHERE
   ENAME LIKE 'S%';

EMP
------------------------------------------------------------------------
<EMP EMPNO="7369" DEPTNO="20"><NAME>SMITH</NAME><JOB>CLERK</JOB></EMP>
<EMP EMPNO="7788" DEPTNO="20"><NAME>SCOTT</NAME><JOB>ANALYST</JOB></EMP>

The EMP element contains two attributes - the employee number and the department number - and two sub elements, the name and the job.

Starting with 10gR2, not only the value of the element could be an expression, but also the name of the element.

SELECT
   XMLELEMENT
   (
      EVALNAME ENAME,
      XMLATTRIBUTES
      (
         EMPNO AS EVALNAME JOB||'_ID'
      )
   ) EMP
FROM
   EMP
WHERE
   ENAME LIKE 'S%';

EMP
-----------------------------------
<SMITH CLERK_ID="7369"></SMITH>
<SCOTT ANALYST_ID="7788"></SCOTT>

The EVALNAMEexpression dynamically sets the element name and the attribute name. The expression must return a character value.