Let the view branch-loan be given to the clerk:
create view branch-loan as
select bname, loan#
Since SQL allows a view name to appear anywhere a relation name may appear, the clerk can write:
insert into branch-loan
values (``SFU'', ``L-307'')
This insertion is represented by an insertion into the actual relation loan, from which the view is constructed. However, we have no value for amount.
This insertion results in (``SFU'', ``L-307'', null) being inserted into the loan relation.
As we saw, when a view is defined in terms of several relations, serious problems can result. As a result, many SQL-based systems impose the constraint that a modification is permitted through a view only if the view in question is defined in terms of one relation in the database.