When you submit a query to an SQL database
using SQL, the database will consult its data dictionary and
access the tables you have requested data from. It will then
put together a "view" based upon the criteria you have defined
in your SQL query.
A "view" is essentially a dynamically generated
"result" table that is put together based upon the parameters you have
defined in your query. For example, you might instruct the
database to give you a list of all the employees in the EMPLOYEES table
with salaries greater than 50,000 USD per year. The database
would check out the EMPLOYEES table and return the requested
list as a "virtual table".
Similarly, a view could be composed of the
results of a query on several tables all at once (sometimes called a "join").
Thus, you
might create a view of all the employees with a salary of
greater than 50K from several stores by cumulating the results from
queries to the EMPLOYEES and STORES databases. The possibilities
are limitless
By the way, many databases allow
you to store "views" in the data dictionary as if they were
physical tables.
