4.6. Privileges

When you create a database object, you become its owner. By default, only the owner of an object can do anything with the object. In order to allow other users to use it, privileges must be granted. (However, users that have the superuser attribute can always access any object.)

There are several different privileges: SELECT, INSERT, UPDATE, DELETE, RULE, REFERENCES, TRIGGER, CREATE, TEMPORARY, EXECUTE, and USAGE. The privileges applicable to a particular object vary depending on the object's type (table, function, etc). For complete information on the different types of privileges supported by EnterpriseDB, refer to the GRANT reference page. The following sections and chapters will also show you how those privileges are used.

The right to modify or destroy an object is always the privilege of the owner only.

To assign privileges, the GRANT command is used. You grant privileges to users so these users can accomplish tasks required for their job. You should grant a privilege only to a user who absolutely requires the privilege to accomplish necessary work. Excessive granting of unnecessary privileges can compromise security. A user can receive a privilege in two different ways:

• You can grant privileges to users explicitly. For example, you can explicitly grant the privilege to insert records into the emp table to the user SCOTT. (Assuming that you have a user named SCOTT in the database).

• You can also grant privileges to a role (a named group of privileges), and then grant the role to one or more users. For example, you can grant the privileges to select, insert, update, and delete records from the emp table to the role named CLERK, which in turn you can grant to the users SCOTT and BRIAN. (Assuming that you have CLERK as a role and BRIAN as a user in the database).

To assign privileges, the GRANT command is used. For example, if joe is an existing user, and emp is an existing table, the privilege to update the table can be granted with

GRANT UPDATE ON emp TO joe;

A better approach is to append the schema name with the object on which we are granting the privileges. So the above statement could be re-written as:

GRANT UPDATE ON public.emp TO joe;

To grant a privilege for selecting from the dept table to an existing ROLE called staff, we would use the following syntax:

GRANT SELECT ON public.dept TO GROUP staff;

To revoke a privilege, use the fittingly named REVOKE command:

REVOKE ALL ON emp FROM staff;

The special privileges of the object owner (i.e., the right to do DROP, GRANT, REVOKE, etc.) are always implicit in being the owner, and cannot be granted or revoked. But the object owner can choose to revoke his own ordinary privileges, for example to make a table read-only for himself as well as others.

Ordinarily, only the object's owner (or a superuser) can grant or revoke privileges on an object. However, it is possible to grant a privilege "GRANT ANY ROLE", which gives the recipient the right to grant it in turn to others. If the grant option is subsequently revoked then all who received the privilege from that recipient (directly or through a chain of grants) will lose the privilege. For details see the GRANT and REVOKE reference pages.