Set Operations (Windows Embedded CE 6.0)

1/6/2010

XML Path Language (XPath) supports the set operation |.

Union Operator

The union operator, or "|", returns the union of two queries; that is, it returns the set of nodes returned for one query combined with the set of nodes that satisfy the other query. Multiple union operators can be combined to union together the results of multiple queries. The union operator preserves document order and does not return duplicates.

The Microsoft implementation extends the union operator to be available anywhere in a query, not just at the top level. To support this behavior, the following constraint is applied to unions: All queries combined with the union operator must be from the same subtree and have the same root.

The following table demonstrates examples of valid and invalid queries based on these constraints.

Valid use of | (same subtree)	Invalid use of | (different subtree)
a | b | c	a | /b | c
/a | /b | /c	a | /b | c
a | .	a | id('C1')
a | b	a | ../b
a | b	a | current()/b
id(x | y)	id(x) | id(y)

Examples

Find all first-names and last-names.

first-name | last-name

Find all books and magazines from a bookstore.

bookstore/(book | magazine)

Find all books and all authors.

book | book/author

Find the first-names, last-names, or degrees from authors within either books or magazines.

(book | magazine)/author/(first-name | last-name | degree)

Find all books with author/first-name equal to "Bob" and all magazines with price less than 10.

book[author/first-name = "Bob"] | magazine[price < 10]

The following will return the first node that matches, not multiple nodes.

id(x | y)

Precedence

Precedence order (from highest precedence to lowest) between Boolean and comparison operators is shown in the following table.

Operator	Meaning
( )	Grouping
[ ]	Filters
/ //	Path operations
< <= > >=	Comparisons
= !=	Comparisons
|	Union
not()	Boolean not
and	Boolean and
or	Boolean or

See Also

Concepts

XPath Syntax
Sample Data
XPath Examples