XQuery aggregate result AND give total - xquery

Question

I have an XML inventory of items.
The inventory lists how much if Item with ID 1 I have, how much of Item with ID 2, etc (think each item ID represents 1 product).
The list, however, is subdivided, depending on what quantity of items of particular type have a particular mark on them.
So, I have let us say:
Item ID Marked? Qty
1 (no) 500
1 ABC 100
1 (no) 50
1 FFFF 333
2 (no) 10000
....
This ir represented in a structure like this:
<Base>
<Item>
<Id>1</Id>
<Qty>500</Qty>
</Item>
<Item>
<Id>1</Id>
<Qty>100</Qty>
<Mark>ABC</Mark>
</Item>
<Item>
<Id>1</Id>
<Qty>50</Qty>
</Item>
<Item>
<Id>1</Id>
<Qty>333</Qty>
<Mark>FFFF</Mark>
</Item>
<Item>
<Id>2</Id>
<Qty>10000</Qty>
</Item>
...
</Base>
Using XQuery transformation I wish to produce, instead of multiple rows per item ID, 1 aggregate row for each item ID, which would list both total sum of quantities per item (both marked and unmarked), and a separate sum for only those quantities of item that are marked (have subtag. I am not concerned about the contents of the individual tags).
In table form what I want would be this:
Item ID Marked Qty Total Qty
1 433 983
2 0 10000
etc.
In actual XML form the transformation should produce something like this:
<Item><Id>1</Id><MarkedQuantity>433</MarkedQuantity><Total>983</Total></Item>
<Item><Id>2</Id><Total>10000</Total></Item>
....
UPD: Edited for clarity.

Answer 1

If you use
for $item in Base/Item
group by $id := $item/Id
order by $id
return <Item>
<Id>{$id}</Id>
{for $marked in $item[Mark]
group by $mark := $marked/Mark
return <Marked name="{$mark}">
{sum($marked/Qty)}
</Marked>
}
<Total>{sum($item/Qty)}</Total>
</Item>
you will get
<Item>
<Id>1</Id>
<Marked name="ABC">100</Marked>
<Total>650</Total>
</Item>
<Item>
<Id>2</Id>
<Total>10000</Total>
</Item>
I am not quite sure you need or want the inner grouping as I am not sure whether there can be different marks you want to distinguish but hopefully it gives you an idea.
If you simply want a total of Marked Items then I think
for $item in Base/Item
group by $id := $item/Id
order by $id
return <Item>
<Id>{$id}</Id>
{if ($item[Mark])
then <MarkedQuantity>{sum($item[Mark]/Qty)}</MarkedQuantity>
else ()
}
<Total>{sum($item/Qty)}</Total>
</Item>
does that.

Answer 2

Turns out that the answer was way easier (as I suspected):
for $item in //Item
let $d := $item/Id
group by $d
order by $d
return <Marked id="{$d}" Total="{ sum($item/Qty) }">{ sum($item[Mark]/Qty) }</Marked>
Basically, give 2 different sums for the same FOR clause: 1 with total sum of items, another with sum of filtered items (those that have Mark child tag in them).
I still do not understand though, why I can't use <Id>{ $d }</Id><Marked>{ sum($item[Mark]/Qty) }</Marked><Total>{ sum($item/Qty) }</Total> - in which case basex complains of finding } where it wanted >
But basically it works.