Java Reference
In-Depth Information
WHERE Last_Name = 'Corleone'
INTERSECT
SELECT First_Name, Last_Name, Street, City, State
FROM Customers
WHERE State = 'NJ';
Data Control Language
The Data Control Language (DCL) provides the tools to manage the database and
control such aspects as user-access privileges. Since a database usually represents
a significant investment in time and effort, managing users is an important aspect of
database management.
A
user
is anyone who has access to the database. Users can be granted different
privileges, ranging from read-only access to a limited portion of the database, all the
way up to unlimited access to the entire RDBMS.
Managing Users
To add individual users to a database, the database administrator must create
database users. This is done using the CREATE USER command. When you create
a user, you can assign a password, certain basic permissions and an expiration date,
all in one command. You can also add the user to an existing user group.
After creating a user, you may need to modify his or her privileges, perhaps to add the
right to modify or delete certain tables or to change the user's password. These
functions are handled using the ALTER USER command.
Finally, you may need to remove an individual's access to the database entirely. This
is done using the DROP USER command.
User privileges
Relational Database Management Systems define sets of privileges that can be
assigned to users. These privileges correspond to actions that can be performed on
objects in the database. User privileges can be assigned at two different levels. Users
can be restricted both at the level of the types o f actions they can perform, such as
READ, MODIFY, or WRITE, and at the level of the types of database objects they can
access.
Access-level privileges can generally be assigned at the following levels:
Global level access to all databases on a given server
Database level access to all tables in a given database
Table-level access to all columns in a given table
