Beginning SQL

10
Views
Views, as the name implies, are queries used to provide users with a specific view of the data in
the database. In doing so, views serve a variety of purposes. They may tie related tables together
and then pull selected fields out that specific users need, or they may pull selected interesting
rows of data from a table that contains other rows of no interest to specific users. They may summarize
large data sets, returning averages, counts, and the like. Relational databases are sets of
data in tables, which, taken alone, are rarely of any use to anyone. Views allow the database
administrator (DBA) to pull fields of interest from tables of interest and return a coherent data set
useful to some specific user or application.
In this chapter, you learn how to build and save views for reuse, how to use views to tie related
data back together, how to use views to narrow or limit the data that users are allowed to see, and
how views may be used for security purposes.
Introducing Views
A normalized database is created by designing tables for each object or event being modeled, with
the fields of each table representing an attribute of the object or event. Once the developer creates
the normalized structure, it becomes necessary to allow users to view specific pieces of data. The
users rarely understand the structure, so the DBA is often tasked with building the views that various
users require. A view is nothing more than a SQL statement that is stored in the database with
an associated name. Views allow the DBA to do the following:
❑ Structure data in a way that users or classes of users find natural or intuitive
❑ Restrict access to the data such that a user can see and (sometimes) modify exactly what
they need and no more
❑ Simplify the DBA’s job by building base data structures that the DBA can use to build
other views in a natural progression
❑ Summarize data for reports