Expecting a cartesian join but did not get 1 (try to understand what is hap

Question

Hello Oracle XML DB gurus,
I have successfully registered my schemas and inserted about 10,000 XML documents into the repository. Now I need to start reporting on the data that is in the documents. Following is a simplified form of my set-up.
I have a table that contain a XML_TYPE column that is schema based.
I will call the table TEST_REF it has two columns: ID number (PK) and XML_DOC which is of the foo schema.
foo schema has the following structure (foo is unbounded).
<DataSet>
<fooList>
<foo>
<val1></val1>
<val2></val2>
</foo>
<foo>
<val1></val1>
<val2></val2>
</foo>
</fooList>
</DataSet>
What I would like to do is select the XML document that I want to extract data from using the ID column. After that I wanted to be able to select all of the data values in /DataSet/fooList/foo from that document (val1 & val2).
I was able to do just that using the following query. However, I do not understand why the following query does not give me a cartesian product when I try to operate on mulitple documents. I'm actually getting exactly what I want, which are the individual data values from each document. I just need to understand what is going on. Does the table() function when used in this fashion perform a inner join for you? I hope this make sense.
select doc.id, extractvalue(Column_value,'/foo/val1') as VALUE1,
extractvalue(Column_value,'/foo/val2') as VALUE2
from test_ref doc,
table(XMLSequence(extract(doc.XML_DOC,'/DataSet/fooList/foo'))) foobar
where doc.id ='1'
------------------------ second where causes the I thought would cause a cartesian join--------------------
where doc.id in (1,2)
Sample data and results when using second where clause:
ID=1
<DataSet>
<fooList>
<foo>
<val1>2</val1>
<val2>22</val2>
</foo>
<foo>
<val1>4</val1>
<val2>44</val2>
</foo>
</fooList>
</DataSet>
ID=2
<DataSet>
<fooList>
<foo>
<val1>1</val1>
<val2>11</val2>
</foo>
<foo>
<val1>3</val1>
<val2>33</val2>
</foo>
</fooList>
</DataSet>
Results:
ID Value1 Value2
1 2 22
1 4 44
2 1 11
2 3 33
If what I'm asking does not make sense please let me know. I'm a newbe with this Oracle XML DB stuff. However, I really like what I have seen so far!
Thanks in advance
Derrick

Answer 1

It's a correlated join...