1. The view update anomaly previously mentioned in Chapter 3 exists also in SQL.

2. An example will illustrate: consider a clerk who needs to see all information in the loan relation except amount.

Let the view branch-loan be given to the clerk:

create view branch-loan as
select bname, loan#
from 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.