For
The for clause allows you to create a table structure from data within a resource or a set of resources. As a result you are no longer bound to one row per resource.
Compare the following two queries:
This first query creates one row per patient, and if that patient has multiple given-names, they will be concatenated into a single field
from Patient
select
name.given
In this second query, you get one row per given-name. If a patient has multiple names or multiple givens in one name, you get a row for each occurence:
from Patient
for name
select
given