In some situations, we might only be interested in which school alice went to, but not her year of graduation. In this case, we would like to be able to perform a query that returns precisely the information we're interested in, without wasting network bandwidth on irrelevant data. Fortunately, user-defined types have this capability.
In order to do this, we simply use a dot operator to specify a single field within a user-defined type that we would like to return. For instance, to retrieve only the school_name field from the alice education field, we can perform the following query:
SELECT "username", "education"."school_name" FROM "users" WHERE "username" = 'alice';
Now, the school name is presented ...
