public Boolean limparCache(){
        try {
            entidadeGerenciamento.createQuery("delete from db_autorizacao where au_id != (select autorizacao from db_aluno)").executeUpdate();
        }catch (Exception e){
            e.printStackTrace();
        }
        return true;
    }

Caused by: Exception [EclipseLink-0] (Eclipse Persistence Services - 2.5.2.v20140319-9ad6abd): org.eclipse.persistence.exceptions.JPQLException
Exception Description: Syntax error parsing [delete from db_autorizacao where au_id != (select autorizacao from db_aluno)].
[75, 75] An identification variable must be provided for a range variable declaration.