XQuery produces incorrect output - xquery

Question

The example xml looks like this:
<sales>
............
<customer custid="108">
<name>NORTH WOODS HEALTH AND FITNESS SUPPLY CENTER</name>
<address>98 LONE PINE WAY</address>
<city>HIBBING</city>
<state>MN</state>
<zip>55649</zip>
<area>612</area>
<phone>566-9123</phone>
<repid>7844</repid>
<creditlimit>8000</creditlimit>
<ord ordid="613">
<orderdate>1987-02-01</orderdate>
<shipdate>1987-02-01</shipdate>
<total>6400</total>
<item itemid="1">
<product_ref ref="100871"/>
<actualprice>5.6</actualprice>
<qty>100</qty>
<itemtot>560</itemtot>
</item>
</ord>
</customer>
<product prodid="100860">
<descrip>ACE TENNIS RACKET I</descrip>
<price>
<stdprice>35</stdprice>
<minprice>28</minprice>
<startdate>1986-06-01</startdate>
</price>
</product>
.........
</sales>
let $product := doc('sales.xml')/sales/product
for $item in doc('sales.xml')/sales/customer/ord/item
where $item/actualprice < $product[#prodid=$item/product_ref/#ref]/price/minprice
return $item
And I get as result this:
<item itemid="1">
<product_ref ref="100861"/>
<actualprice>35</actualprice>
<qty>1</qty>
<itemtot>35</itemtot>
</item>
<item itemid="3">
<product_ref ref="101863"/>
<actualprice>10</actualprice>
<qty>150</qty>
<itemtot>1500</itemtot>
</item>
<item itemid="7">
<product_ref ref="101863"/>
<actualprice>12.5</actualprice>
<qty>200</qty>
<itemtot>2500</itemtot>
</item>
<item itemid="5">
<product_ref ref="101863"/>
<actualprice>9</actualprice>
<qty>100</qty>
<itemtot>900</itemtot>
</item>
But the items with ref=101863 are not right. Only the item with id=5 is less then minprice.
Why does this error occur? Tried a lot of different queries but it gives me always the same result.
It works fine with ref=100861.

Answer 1

Assuming the query isn't schema-aware, you are comparing the two prices as strings, not as numbers. You need to convert both to numbers before comparison.