Empty results when filtering based on position in XQuery - sql-server

Question

I tried to print the details of 3rd and 4th products in the catalog, but I am getting empty results.
XML input:
<catalog>
<product dept="WMN">
<number>557</number>
<name language="en">Fleece Pullover</name>
<colorChoices>navy black</colorChoices>
</product>
<product dept="ACC">
<number>563</number>
<name language="en">Floppy Sun Hat</name>
</product>
<product dept="ACC">
<number>443</number>
<name language="en">Deluxe Travel Bag</name>
</product>
<product dept="MEN">
<number>784</number>
<name language="en">Cotton Dress Shirt</name>
<colorChoices>white gray</colorChoices>
<desc>Our <i>favorite</i> shirt!</desc>
</product>
</catalog>
what I tried:
SELECT xDoc.query(' for $prod in //product
let $x:=$prod
return (<Item>{data($x[3])}{data($x[4])}</Item>)')
FROM AdminDocs
where id=6
Output displayed:
<Item />
<Item />
<Item />
<Item />

Answer 1

This defines a loop over all products:
for $prod in //product
For each of those products, you return the third and fourth node out of a sequence of a single product, which obviously will yield empty nodes:
let $x:=$prod
return (<Item>{data($x[3])}{data($x[4])}</Item>)
For a better understanding, return the whole product node each time:
for $prod in //product
return <item>{ $prod }</item>
Which will result in something like this:
<item>
<product dept="WMN">
<number>557</number>
<name language="en">Fleece Pullover</name>
<colorChoices>navy black</colorChoices>
</product>
</item>
<item>
<product dept="ACC">
<number>563</number>
<name language="en">Floppy Sun Hat</name>
</product>
</item>
<item>
<product dept="ACC">
<number>443</number>
<name language="en">Deluxe Travel Bag</name>
</product>
</item>
<item>
<product dept="MEN">
<number>784</number>
<name language="en">Cotton Dress Shirt</name>
<colorChoices>white gray</colorChoices>
<desc>Our <i>favorite</i> shirt!</desc>
</product>
</item>
And each of those <product/> elements being a $prod[1]. Try:
for $prod in //product
return <item>{ $prod[1] }</item>
which will return the exactly same result, compared to
for $prod in //product
return <item>{ $prod[2] }</item>
(or any other positional predicate) resulting in empty <item/> nodes.
Finally, to return only the third and fourth products, shift the positional predicate into the for loop argument:
for $prod in //product[position() = 3 or position() = 4]
return <item>{ $prod }</item>
(and apply data(...) as needed, but I'd guess it won't yield the results you expect here).