It is frequently convenient to group users together to ease management of privileges: that way, privileges can be granted to, or revoked from, a group as a whole. In PostgreSQL this is done by creating a role that represents the group, and then granting membership in the group role to individual user roles.
To set up a group role, first create the role:
CREATE ROLE name;
Typically a role being used as a group would not have the LOGIN attribute, though you can set it if you wish.
Once the group role exists, you can add and remove members using the GRANT and REVOKE commands:
GRANTgroup_roleTOrole1, ... ; REVOKEgroup_roleFROMrole1, ... ;
You can grant membership to other group roles, too (since there isn't really any distinction between group roles and non-group roles). The database will not let you set up circular membership loops. Also, it is not permitted to grant membership in a role to PUBLIC.
The members of a group role can use the privileges of the role in two ways. First, every member of a group can explicitly do SET ROLE to temporarily “become” the group role. In this state, the database session has access to the privileges of the group role rather than the original login role, and any database objects created are considered owned by the group role not the login role. Second, member roles that have the INHERIT attribute automatically have use of the privileges of roles of which they are members, including any privileges inherited by those roles. As an example, suppose we have done:
CREATE ROLE joe LOGIN INHERIT; CREATE ROLE admin NOINHERIT; CREATE ROLE wheel NOINHERIT; GRANT admin TO joe; GRANT wheel TO admin;
Immediately after connecting as role joe, a database session will have use of privileges granted directly to joe plus any privileges granted to admin, because joe “inherits” admin's privileges. However, privileges granted to wheel are not available, because even though joe is indirectly a member of wheel, the membership is via admin which has the NOINHERIT attribute. After:
SET ROLE admin;
the session would have use of only those privileges granted to admin, and not those granted to joe. After:
SET ROLE wheel;
the session would have use of only those privileges granted to wheel, and not those granted to either joe or admin. The original privilege state can be restored with any of:
SET ROLE joe; SET ROLE NONE; RESET ROLE;
The SET ROLE command always allows selecting any role that the original login role is directly or indirectly a member of. Thus, in the above example, it is not necessary to become admin before becoming wheel.
In the SQL standard, there is a clear distinction between users and roles, and users do not automatically inherit privileges while roles do. This behavior can be obtained in PostgreSQL by giving roles being used as SQL roles the INHERIT attribute, while giving roles being used as SQL users the NOINHERIT attribute. However, PostgreSQL defaults to giving all roles the INHERIT attribute, for backward compatibility with pre-8.1 releases in which users always had use of permissions granted to groups they were members of.
The role attributes LOGIN, SUPERUSER, CREATEDB, and CREATEROLE can be thought of as special privileges, but they are never inherited as ordinary privileges on database objects are. You must actually SET ROLE to a specific role having one of these attributes in order to make use of the attribute. Continuing the above example, we might choose to grant CREATEDB and CREATEROLE to the admin role. Then a session connecting as role joe would not have these privileges immediately, only after doing SET ROLE admin.
To destroy a group role, use DROP ROLE:
DROP ROLE name;
Any memberships in the group role are automatically revoked (but the member roles are not otherwise affected).