XQuery

Chapter 9. Advanced Queries

Now that you are an expert on the syntax of XQuery expressions, let's look at some more-advanced queries. This chapter describes syntax and techniques for some commonly requested query capabilities. You may have these same requirements for your queries, but even if you don't, this chapter will show you some creative ways to apply XQuery syntax.

Copying Input Elements with Modifications

Often you will want to include elements from an input document, but with minor modifications. For example, you may wish to eliminate or add attributes, or change their names. However, the XQuery language does not have specific update capability, nor does it have any special functions or operators that perform these minor modifications. For example, there is no direct syntax that means "select all the product elements, but leave out their dept attributes."

The good news is that you can accomplish these modifications by "reconstructing" the elements. For example, you can write a query to construct a new product element and include all the children and attributes (except dept) of the original product element in the input document. Even better, you can write a user-defined function that uses computed constructors to handle these modifications in the general case. This section describes some common modifications and provides useful functions to handle these cases.

Note that these functions are intended to change the way elements and attributes appear in the results of a query, ...