Database Reference
In-Depth Information
15.7 Summary and Concluding Remarks
Here is a summary of what was covered in this chapter:
•
SQL is a powerful language, but not without limitations. The first
is that SQL is a database language by design and intent. It does
not include features for building complex user interfaces, because
it was not intended to.
•
You are not allowed to use the
Order-By-Clause
on SQL views.
Additionally, a view is not updateable if it includes the use of the
set operator UNION, INTERSECT, or JOIN.
•
Some implementations of SQL do not provide the designer the
flexibility of specifying which attribute(s) of a referenced table are
to be considered when a foreign key constraint is defined.
•
Some implementations of SQL exhibit a superfluous enforcement
of the referential integrity rule with respect to update of non-key
attributes of rows in a referenced relation.
•
You are not allowed to define a calculated column in terms of
another calculated column in the same query, or to reference a
calculated column in the same
Select
statement.
•
It appears that the if-then construct is not widely supported
in SQL.
Fortunately, there is a work-around for each limitation. This is perhaps why SQL is
so popular: its benefits far outweigh its limitations. We can therefore expect that SQL will
continue to be the universal database language a long time yet.
This brings us to the end of our study of SQL. The next five chapters provide an
overview of five commonly used DBMS suites.
15.8 Review Questions
1.
What are the programming limitations of SQL? As a software
engineer, how do you make up for these limitations?
2.
Discuss the limitations of SQL with respect to logical views.
What are the implications of these limitations?
3.
What problems relating to referential integrity are often
present in implementations of SQL? How are these problems
addressed in Oracle 10g?
4.
Describe the SQL limitation on calculated columns. Carefully
explain how it can be circumvented.
