Expressions

XQuery supports several kinds of expressions for working with XML data.

Expression evaluation and processing
A number of operations are often included in the processing of expressions. These operations include extracting atomic values from nodes and using type promotion and subtype substitution to obtain values of an expected type.
Primary expressions
Primary expressions are basic primitives of the language.
Path expressions
Path expressions locate nodes within an XML tree. Path expressions in XQuery are based on the syntax of XPath 2.0.
Sequence expressions
Sequence expressions construct, filter, and combine sequences of items. Sequences are never nested. For example, combining the values 1, (2, 3), and ( ) into a single sequence results in the sequence (1, 2, 3).
Filter expressions
A filter expression consists of a primary expression that is followed by zero or more predicates. The predicates, if present, filter the result of the primary expression.
Arithmetic expressions
Arithmetic expressions perform operations that involve addition, subtraction, multiplication, division, and modulus.
Comparison expressions
Comparison expressions compare two values. XQuery provides general comparisons, value comparisons, and node comparisons.
Logical expressions
Logical expressions return the boolean value true if both of two expressions are true, or if one or both of two expressions are true. The operators that are used in logical expressions include and and or.
XQuery constructors
XQuery constructors create XML structures within a query. .
FLWOR expressions
FLWOR expressions iterate over sequences and bind variables to intermediate results.
Conditional expressions
Conditional expressions use the keywords if, then, and else to evaluate one of two expressions based on whether the value of a test expression is true or false.
Basic updating expressions
Using the basic XQuery updating expressions, you can create complex updating expressions to update existing XML data.
Castable expressions
Castable expressions test whether a value can be cast to a specific data type. If the value can be cast to the data type, the castable expression returns true. Otherwise, the expression returns false.
Regular expressions
A regular expression is a sequence of characters that act as a pattern for matching and manipulating strings. Regular expressions are used in the fn:matches, fn:replace, and fn:tokenize functions.

Parent topic: XQuery prologs and expressions