Reading XML element occurrences using PL SQL

Question

I have this XML.

<a>
   <b>b1</b>
   <c>c1</c>
   <b>b2</b>
   <c>c2</c2>
</a>

I want to be able to extract the values of elements 'b' and 'c' using PL\SQL. I'm using Oracle 10g.

So far I have this,

  SELECT   XML.b                    
       , XML.c
    FROM XMLTable (
           '/a' PASSING p_xml
              COLUMNS
                 b            VARCHAR(2) PATH 'b/.'
               , c            VARCHAR(2) PATH 'c/.'
    ) XML

But I keep getting this error:

19279. 00000 -  "XQuery dynamic type mismatch: expected singleton sequence - got multi-item sequence" 
*Cause:    The XQuery sequence passed in had more than one item.
*Action:   Correct the XQuery expression to return a single item sequence.

Then I tried this:

  SELECT   XML.b                    
         , XML1.c
    FROM XMLTable (
           '/a/b' PASSING p_xml
              COLUMNS
                 b            VARCHAR(2) PATH '.'
    ) XML,
        XMLTable (
           '/a/c' PASSING p_xml
              COLUMNS
                 c            VARCHAR(2) PATH '.'
    ) XML1

But the results were:

b1,c1
b1,c2
b2,c1
b2,c2

When I want only: b1 c1 b2 c2

Can you guys help me out?

newuserua_ext · Accepted Answer · 2015-02-25 12:33:20Z

1

I didnt run it but as far as i see below code should work ;

DECLARE
vs_Xml VARCHAR2(32000):= '<INPUT>
  <A>
    <B>1</B>
  </A>
  <A>
    <B>2</B>
  </A>
</INPUT>';

vx_ParameterList   XMLTYPE;
vx_Parameter       XMLTYPE;
vn_ParameterIndex  NUMBER;
vs_Key             VARCHAR2(64);
vs_XPath           VARCHAR2(255);
vs_Value           VARCHAR2(10000);

BEGIN
vx_ParameterList := xmltype(vs_Xml);
vn_ParameterIndex := 1;
vs_XPath := '/INPUT/A'; 

WHILE vx_ParameterList.existsNode(vs_XPath || '[' || vn_ParameterIndex || ']') = 1 LOOP
  vx_Parameter := vx_ParameterList.extract(vs_XPath || '[' || vn_ParameterIndex || ']');

  vs_Value := vx_Parameter.extract('//B/text()').GetStringVal();
  vn_ParameterIndex := vn_ParameterIndex + 1;

  dbms_output.put_line(vs_Value);
END

answered Feb 25, 2015 at 12:33

newuserua_ext

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Comments

collapsar · Accepted Answer · 2015-02-25 14:13:21Z

You have to adjust the xquery expression in the XMLTABLE command. The basic idea is to produce a stream of xml records each of which can be mapped to columns of a database record.

The obstacle in the original xml is that the xpath axis /a returns - phrased sloppily - the content of all xml records.

The solution is to build an iterator over /a that delivers the xml records one-by-one (technically: wrapped in an synthetic x element).

The following can be issued from sqlplus:

      SELECT   myxml.b
           ,   myxml.c                            
        FROM XMLTable (
'for $i in (1, let $x := fn:count(/a/b) return $x )
 let $b := /a/b[$i], $c := /a/c[$i]
 return <x>
           <b>{$b}</b>
           <c>{$c}</c>
        </x>
' PASSING XMLTYPE(
'<a>
   <b>b1</b>
   <c>c1</c>
   <b>b2</b>
   <c>c2</c>
</a>')
                  COLUMNS
                     b            VARCHAR(2) PATH '/x/b'
                   , c            VARCHAR(2) PATH '/x/c'
        ) myxml
;

Update

In order to allow for arbitrary number of b/c children, the following line

for $i in (1, let $x := fn:count(/a/b) return $x )

replaces the original

for $i in (1, 2)

in the above expression.

Reference

More info about XQuery syntax can be found in the W3c spec (deep-links to the syntax doc forthe so-called FWLOR expressions).

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