Sybase 12.4.2 User Manual

Working with views

 

Similarities between 
views and base tables

Views are similar to the permanent tables of the database (a permanent table is 
also called a base table) in many ways:

•

You can assign access permissions to views just as to base tables.

•

You can perform 

SELECT 

queries on views.

•

You can perform 

INSERT 

and 

DELETE 

operations on some views.

•

You can create views based on other views.

Differences between 
views and permanent 
tables

There are some differences between views and permanent tables:

•

You cannot create indexes on views.

•

You cannot perform 

INSERT

, 

DELETE

, and 

UPDATE

 operations on all 

views.

•

You cannot assign integrity constraints and keys to views.

•

Views refer to the information in base tables, but do not hold copies of that 
information. Views are recomputed each time you invoke them.

Benefits of tailoring 
access

Views are used to tailor access to data in the database. Tailoring access serves 
several purposes:

By not allowing access to information that is not 

relevant.

By presenting users and application developers 

with data in a more easily understood form than in the base tables.

By centralizing in the database the definition 

of common queries.

A 

SELECT 

statement operates on one or more tables and produces a result set 

that is also a table: just like a base table, a result set from a 

SELECT 

query has 

columns and rows. A view gives a name to a particular query, and holds the 
definition in the database system tables.

Example

Suppose that you frequently need to list the number of employees in each 
department. You can get this list with the following statement:

SELECT dept_ID, count(*)

FROM employee

GROUP BY dept_ID

You can create a view containing the results of this statement as follows: