XMLAgg alias: Inconsistent between 10g (10.2.0.4) and 11g (10.2.0.3)

Question

Hi All,
We're seeing inconsistent behavior between 10g (10.2.0.4) and 11g (10.2.0.3) when aliasing a nested select statement that returns an XMLAgg.
Not sure if this is an instance of Oracle correcting behavior or if this should be considered a bug.
Sample query:
SELECT xmlelement("ItemData",
(SELECT xmlagg(
XMLELEMENT("Item", x.item)
FROM (SELECT 'item1' item FROM dual
UNION ALL
SELECT 'item2' item FROM dual) x
) AS "Items" -- in10g alias on nested select is used for grouping element name; however in 11g alias is ignored
).extract('/') xml
FROM dual;
10g result:
<ItemData>
<Items>
<Item>item1</Item>
<Item>item2</Item>
</Items>
</ItemData>
11g result:
<ItemData><Item>item1</Item><Item>item2</Item></ItemData>
The issue is the missing “Items” element, not the pretty print.
Alternate 1:
I’ve found that I can use SYS_XMLAGG together with XMLFormat so that it works in either 10g or 11g -- When using in 10g the nested select statement cannot be aliased otherwise a duplicate Items element is created
SELECT xmlelement("ItemData",
(SELECT sys_xmlagg(
XMLELEMENT("Item", x.item),
XMLFormat('Items')
FROM (SELECT 'item1' item FROM dual
UNION ALL
SELECT 'item2' item FROM dual) x
) -- Cannot alias in 10g otherwise a grouping element is created
).extract('/') xml
FROM dual;
10g result:
<ItemData>
<Items>
<Item>item1</Item>
<Item>item2</Item>
</Items>
</ItemData>
11g result:
<ItemData><Items>
<Item>item1</Item>
<Item>item2</Item>
</Items>
</ItemData>
Alternate 2:
Another alternative is using an additional XMLElement tag to create the grouping element “Items” (As above select statement w/ XMLAGG cannot be aliased)
SELECT xmlelement("ItemData",
xmlElement("Items",
(SELECT xmlagg(
XMLELEMENT("Item", x.item)
FROM (SELECT 'item1' item FROM dual
UNION ALL
SELECT 'item2' item FROM dual) x
)-- Cannot alias in 10g otherwise a grouping element is created
).extract('/') xml
FROM dual;
10g result:
<ItemData>
<Items>
<Item>item1</Item>
<Item>item2</Item>
</Items>
</ItemData>
11g result:
<ItemData><Items><Item>item1</Item><Item>item2</Item></Items></ItemData>

Answer 1

Hi,
This issue was discussed a couple of years ago : {thread:id=1093561}
IMO, the correct behaviour is the 11g's.
The Alternative #2 you mentioned above using XMLElement (or XMLForest) should be the only way to correctly deal with this situation in any version.
Just curious, where did you first see/learn that aliasing a subquery should create automatically an additional wrapping element?