Chapter 7. Sorting and Grouping
This chapter explains how to sort and group data from input documents. It covers sorting in FLWORs, grouping results together, and calculating summary values by using aggregate functions.
Sorting in XQuery
Path expressions, which are most often used to select elements and attributes from input documents, always return items in document order. FLWORs by default return results based on the order of the sequence specified in the
for clause, which is also often document order if a path expression was used.
You can sort data in an order other than document order by using the
order by clause of the FLWOR. Therefore, in some cases it is necessary to use a FLWOR where it would not otherwise be necessary. For example, if you simply want to select all your items from an order, you can use the path expression
doc("order.xml")//item. However, if you want to sort those items based on their
num attribute, the most straightforward way to do this is using a FLWOR with an
order by clause. The other alternative is to use the
sort function, described in “The
order by Clause
Example 7-1 shows an
order by clause in a FLWOR.
Example 7-1. The
order by clause
The results will be sorted by item number. The syntax of an
order by clause is shown in Figure 7-1.
order by clause is made up of one or more ordering specifications, separated by commas, each of which consists of an expression and an ...