C# 0 The Complete Reference

ch1

,

ch2

 produced by each iteration of the inner 

from

. Thus, a 

ChrPair

 is 

produced in which each possible combination of characters is obtained.

Another common use of a nested 

from

 is to iterate over a data source that is contained 

within another data source. An example of this is found in the section, “Use 

let

 to Create 

a Variable in a Query,” later in this chapter.

Group Results with group

One of the most powerful query features is provided by the 

group

 clause because it enables 

you to create results that are grouped by keys. Using the sequence obtained from a group, 

you can easily access all of the data associated with a key. This makes 

group

 an easy and 

effective way to retrieve data that is organized into sequences of related items. The 

group

clause is one of only two clauses that can end a query. (The other is