18.4. role membership

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:

grant group_role to role1, ... ; revoke group_role from role1, ... ;

you can grant membership to other group roles, too (since there isn't really any distinction between group roles and non-group roles). the only restriction is that you can't set up circular membership loops.

the members of a role can use the privileges of the group 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 privileges of roles they are members of. 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 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 well 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). note however that any objects owned by the group role must first be dropped or reassigned to other owners; and any permissions granted to the group role must be revoked.