Postgres Plus Advanced Server Oracle Compatibility Developer's Guide :
DROP ROLE -- remove a database role
DROP ROLE name [ CASCADE ]
DROP ROLE removes the specified role. To drop a superuser role, you must be a superuser yourself; to drop non-superuser roles, you must have CREATEROLE privilege.
A role cannot be removed if it is still referenced in any database of the cluster; an error will be raised if so. Before dropping the role, you must drop all the objects it owns (or reassign their ownership) and revoke any privileges the role has been granted.
It is not necessary to remove role memberships involving the role; DROP ROLE automatically revokes any memberships of the target role in other roles, and of other roles in the target role. The other roles are not dropped nor otherwise affected.
Alternatively, if the only objects owned by the role belong within a schema that is owned by the role and has the same name as the role, the CASCADE option can be specified. In this case the issuer of the DROP ROLE name CASCADE command must be a superuser and the named role, the schema, and all objects within the schema will be deleted.
The name of the role to remove.
If specified, also drops the schema owned by, and with the same name as the role (and all objects owned by the role belonging to the schema) as long as no other dependencies on the role or the schema exist.
To drop a role:
DROP ROLE admins;