我是 postgres 的新手（以及数据库信息系统的新手）。我在我的数据库上运行了以下 sql 脚本：

create table cities (
id serial primary key,
name text not null
);

create table reports (
id serial primary key,
cityid integer not null references cities(id),
reportdate date not null,
reporttext text not null
);

create user www with password 'www';

grant select on cities to www;
grant insert on cities to www;
grant delete on cities to www;

grant select on reports to www;
grant insert on reports to www;
grant delete on reports to www;

grant select on cities_id_seq to www;
grant insert on cities_id_seq to www;
grant delete on cities_id_seq to www;

grant select on reports_id_seq to www;
grant insert on reports_id_seq to www;
grant delete on reports_id_seq to www;

当用户 www 尝试：

insert into cities (name) values ('London');

我收到以下错误：

ERROR: permission denied for sequence cities_id_seq

我知道问题出在串行类型上。这就是为什么我将 *_id_seq 的选择、插入和删除权限授予 www。然而，这并不能解决我的问题。我错过了什么？