XPath expressions in aggreation functions behave different than I expect

Question

Hi,
I'm having the following very simple schema:
<?xml version="1.0" encoding="ISO-8859-1" ?>
<xs:schema xmlns:xs="http://www.w3.org/2001/XMLSchema">
<xs:element name="a" type="AType" />
<xs:complexType name="AType">
<xs:sequence>
<xs:element name="b" type="BType" />
</xs:sequence>
</xs:complexType>
<xs:complexType name="BType">
<xs:sequence>
<xs:element name="c" type="CType" minOccurs="1" maxOccurs="unbounded" />
</xs:sequence>
</xs:complexType>
<xs:complexType name="CType">
<xs:all minOccurs="0">
<xs:element name="d1" type="xs:double" />
<xs:element name="d2" type="xs:double" />
<xs:element name="d3" type="xs:double" />
<xs:element name="d4" type="xs:double" />
<xs:element name="d5" type="xs:double" />
<xs:element name="d6" type="xs:double" />
</xs:all>
</xs:complexType>
</xs:schema>
Which I loaded using the following code:
declare
l_bfile bfile;
begin
l_bfile := bfilename('DIR_TEMP', 'simple.xsd');
dbms_lob.open(l_bfile);
dbms_xmlschema.registerschema('http://localhost/simple.xsd',l_bfile);
dbms_lob.close(l_bfile);
end;
Then I created the table "simple" as follows:
CREATE TABLE simple OF XMLTYPE XMLSchema "http://localhost/simple.xsd" ELEMENT "a";
And I loaded the following XML document:
<?xml version="1.0"?><a>< b>
<c><d1>0</d1></c>
<c><d1>1</d1></c>
<c><d1>2</d1></c>
<c><d1>3</d1></c>
<c><d1>4</d1></c>
<c><d1>5</d1></c>
<c><d1>6</d1></c>
<c><d1>7</d1></c>
<c><d1>8</d1></c>
<c><d1>9</d1></c>
</b></a>
Which was loaded by the following code:
DECLARE
file bfile;
charContent clob := ' ';
targetFile bfile;
charset_id number := 0;
src_offset number := 1;
dst_offset number := 1;
lang_ctx number := DBMS_LOB.default_lang_ctx;
warning number;
BEGIN
DBMS_OUTPUT.enable(10000);
file := bfilename('DIR_TEMP','simple.xml');
targetFile := file;
DBMS_LOB.fileopen(targetFile,DBMS_LOB.file_readonly);
DBMS_LOB.loadclobfromfile(charContent,targetFile,DBMS_LOB.getLength(targetFile),src_offset, dst_offset, charset_id, lang_ctx, warning);
DBMS_LOB.fileclose(targetfile);
INSERT INTO simple VALUES (xmltype(charContent));
END;
The function to be executed is the avg of d1. The solution if of course 4.5.
The following queries give the correct answer:
SELECT XMLQuery('for $i in /a return avg($i//d1)' PASSING OBJECT_VALUE RETURNING CONTENT) FROM simple;
SELECT XMLQuery('for $i in /a return avg(//d1)' PASSING OBJECT_VALUE RETURNING CONTENT) FROM simple;
SELECT XMLQuery('for $i in /a let $t := //d1 return avg($t)' PASSING OBJECT_VALUE RETURNING CONTENT) FROM simple;
However, when I execute any of the following expressions, they return nothing (or to be exact: an empty row):
SELECT XMLQuery('for $i in /a return avg($i/b/c/d1)' PASSING OBJECT_VALUE RETURNING CONTENT) FROM simple;
SELECT XMLQuery('for $i in /a return avg($i//c/d1)' PASSING OBJECT_VALUE RETURNING CONTENT) FROM simple;
SELECT XMLQuery('for $i in /a return avg(//c/d1)' PASSING OBJECT_VALUE RETURNING CONTENT) FROM simple;
SELECT XMLQuery('for $i in /a let $t := //c/d1 return avg($t)' PASSING OBJECT_VALUE RETURNING CONTENT) FROM simple;
I'm expecting that avg($i//c/d1) selects all d1 elements contained in a c element within the context of $i and return the average of those d1s. However, it doesn't seem to do so.
When I remove the "avg" in the last query:
SELECT XMLQuery('for $i in /a let $t := //c/d1 return $t' PASSING OBJECT_VALUE RETURNING CONTENT) FROM simple;
it does return a list of all d1 elements, as I expect. However the aggragation function doesn't return the value as expected. I've tested with more aggregation functions (eg. min, max) and all are having the same effects.
Can anyone explain me what I'm missing here, or point me to some documentation which explains it?
I'm running:
SQL*Plus: Release 10.2.0.3.0 - Production
on
Oracle Database 10g Enterprise Edition Release 10.2.0.3.0 - Production
With the Partitioning, OLAP and Data Mining options
null
Message was edited by:
Tijink

Answer 1

Did you also try to create the XMLSchema and the table and run the queries against that?Still, no difference for me:
michaels>  declare
   l_clob   clob
      := '<?xml version="1.0" encoding="ISO-8859-1" ?>
<xs:schema xmlns:xs="http://www.w3.org/2001/XMLSchema">
<xs:element name="a" type="AType" />
<xs:complexType name="AType">
<xs:sequence>
<xs:element name="b" type="BType" />
</xs:sequence>
</xs:complexType>
<xs:complexType name="BType">
<xs:sequence>
<xs:element name="c" type="CType" minOccurs="1" maxOccurs="unbounded" />
</xs:sequence>
</xs:complexType>
<xs:complexType name="CType">
<xs:all minOccurs="0">
<xs:element name="d1" type="xs:double" />
<xs:element name="d2" type="xs:double" />
<xs:element name="d3" type="xs:double" />
<xs:element name="d4" type="xs:double" />
<xs:element name="d5" type="xs:double" />
<xs:element name="d6" type="xs:double" />
</xs:all>
</xs:complexType>
</xs:schema>';
begin
   dbms_xmlschema.registerschema (schemaurl      => 'http://localhost/simple.xsd',
                                  schemadoc      => l_clob,
                                  gentypes       => false
end;
PL/SQL procedure successfully completed.
michaels>  create table simple of xmltype xmlschema "http://localhost/simple.xsd" element "a"
Table created.
michaels>  insert into simple
     values (xmltype
                ('<?xml version="1.0"?><a><b>
            <c><d1>0</d1></c>
            <c><d1>1</d1></c>
            <c><d1>2</d1></c>
            <c><d1>3</d1></c>
            <c><d1>4</d1></c>
            <c><d1>5</d1></c>
            <c><d1>6</d1></c>
            <c><d1>7</d1></c>
            <c><d1>8</d1></c>
            <c><d1>9</d1></c></b></a>'
1 row created.
michaels>  select xmlquery('for $i in /a return avg($i//d1)' passing  object_value returning content).getnumberval() res from simple
union all
select xmlquery('for $i in /a return avg(//d1)' passing  object_value returning content).getnumberval() res from simple
union all
select xmlquery('for $i in /a let $t := //d1 return avg($t)' passing  object_value returning content).getnumberval() res from simple
union all
select xmlquery('for $i in /a return avg($i/b/c/d1)' passing  object_value returning content).getnumberval() res from simple
union all
select xmlquery('for $i in /a return avg($i//c/d1)' passing  object_value returning content).getnumberval() res from simple
union all
select xmlquery('for $i in /a return avg(//c/d1)' passing  object_value returning content).getnumberval() res from simple
union all
select xmlquery('for $i in /a  let $t := //c/d1 return avg($t)' passing  object_value returning content).getnumberval() res from simple
       RES
       4,5
       4,5
       4,5
       4,5
       4,5
       4,5
       4,5
7 rows selected.