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This chapter is from the book

This chapter is from the book

In Brief

  • XQuery is a declarative language. After an item is defined within a given scope (such as a program block or function), the item can't be redefined within that scope.

  • The let statement defines a function that has a constant value.

  • The for keyword assigns to a temporary variable successive values in a sequence.

  • The return keyword takes the sets defined by for and let statements and turns them into a result—XML, a sequence of values, a single string expression, and so on.

  • The where keyword lets you define conditions about which data should be chosen. It creates a predicate cause that narrows a range of potential options.

  • The order by command follows for expressions (and where expressions where they exist) and indicates for a given set of data the order in which the data is output. When it is not explicitly specified with order by, the output order depends on the system architecture.

  • XQuery works with XPath's conditional if/then/else keywords to create logical expressions.

  • XQuery provides many built-in functions and also lets you create user-definable functions. Anything passed into an XQuery function is passed by value, not reference, and a function must always return something of value.

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