Select the Output element from the palette and place it below the priceelement.
从调色板中选择 Output 元素,并将其放在 price 元素的下面。
2
If you know that a book has at most one priceelement, you can write the query using XQuery value comparisons, which force the comparison operands to be singletons.
For example, you could define a Priceelement that is always a floating-point number or a PersonName element that has FirstName and LastName sub-elements that are both strings.