子查询返回多列 - 或近似值

Question

我有一个有趣的问题，但是我不知道如何更好地表达它，而不是说我有一个需要返回多个列的子查询。当我尝试执行此操作时，PostgreSQL 会抛出错误，因此虽然我的 SQL 在我看来在逻辑上有些合理，但显然有更好的方法来执行此操作。我正在尝试将用户权限合并到一个表中（希望将其放入视图甚至某种“物化视图”中）。这是我的表：

CREATE TABLE users (
  user_id integer NOT NULL,
  username character varying(32) NOT NULL,
  passwd character varying(32) NOT NULL,
  dept_id integer NOT NULL,
  last_activity timestamp with time zone NOT NULL DEFAULT now(),
  CONSTRAINT "pk-users-user_id" PRIMARY KEY (user_id)
);

CREATE TABLE groups (
  group_id integer NOT NULL,
  group_name character varying(32) NOT NULL,
  add_posts integer NOT NULL DEFAULT 0,
  remove_posts integer NOT NULL DEFAULT 0,
  modify_users integer NOT NULL DEFAULT 0,
  add_users integer NOT NULL DEFAULT 0,
  delete_users integer NOT NULL DEFAULT 0,
  CONSTRAINT "pk-groups-group_id" PRIMARY KEY (group_id)
);

CREATE TABLE user_groups (
  user_id integer NOT NULL,
  group_id integer NOT NULL,
  CONSTRAINT "fk-user_groups-group_id" FOREIGN KEY (group_id)
      REFERENCES groups (group_id) MATCH SIMPLE
      ON UPDATE NO ACTION ON DELETE NO ACTION,
  CONSTRAINT "fk-user_groups-user_id" FOREIGN KEY (user_id)
      REFERENCES users (user_id) MATCH SIMPLE
      ON UPDATE NO ACTION ON DELETE NO ACTION
);

CREATE TABLE user_rights (
  user_id integer NOT NULL,
  add_posts integer NOT NULL DEFAULT 0,
  remove_posts integer NOT NULL DEFAULT 0,
  modify_users integer NOT NULL DEFAULT 0,
  add_users integer NOT NULL DEFAULT 0,
  delete_users integer NOT NULL DEFAULT 0,
  CONSTRAINT "fk-user_rights-user_id" FOREIGN KEY (user_id)
      REFERENCES users (user_id) MATCH SIMPLE
      ON UPDATE NO ACTION ON DELETE CASCADE
);

以及一些填充它们的数据：

INSERT INTO users(user_id, username, passwd, dept_id) VALUES (1, 'nicole','123456',12);
INSERT INTO users(user_id, username, passwd, dept_id) VALUES (2, 'john','324634',11);
INSERT INTO users(user_id, username, passwd, dept_id) VALUES (3, 'susan','61236',14);
INSERT INTO users(user_id, username, passwd, dept_id) VALUES (4, 'mary','1213612',2);
INSERT INTO user_rights(user_id, add_posts, remove_posts, modify_users, add_users, delete_users) VALUES (1,0,0,1,1,1);
INSERT INTO user_rights(user_id, add_posts, remove_posts, modify_users, add_users, delete_users) VALUES (2,1,1,1,1,1);
INSERT INTO user_rights(user_id, add_posts, remove_posts, modify_users, add_users, delete_users) VALUES (3,0,0,0,0,0);
INSERT INTO user_rights(user_id, add_posts, remove_posts, modify_users, add_users, delete_users) VALUES (4,0,0,0,0,0);
INSERT INTO groups(group_id, group_name, add_posts, remove_posts, modify_users, add_users, delete_users) VALUES (1,'Poster',1,1,0,0,0);
INSERT INTO groups(group_id, group_name, add_posts, remove_posts, modify_users, add_users, delete_users) VALUES (2,'User Mgr',0,0,1,1,1);
INSERT INTO groups(group_id, group_name, add_posts, remove_posts, modify_users, add_users, delete_users) VALUES (3,'Admin',1,1,1,1,1);
INSERT INTO user_groups(user_id, group_id) VALUES (1,1);
INSERT INTO user_groups(user_id, group_id) VALUES (2,2);
INSERT INTO user_groups(user_id, group_id) VALUES (3,2);
INSERT INTO user_groups(user_id, group_id) VALUES (4,3);
INSERT INTO user_groups(user_id, group_id) VALUES (1,2);

我想做的是创建一个查询来计算用户可能拥有的有效权限。用户存储在（您猜对了）“用户”表中。 “groups”中的组，无论用户可能被分配到哪个组，都在“user_groups”中。最后，每个用户都可以拥有应覆盖组权限的个人权限 - 这些权限存储在“user_rights”中。

我可以使用以下命令提取所有这些信息的查询（是的，我知道这很丑陋）：

select
  max(add_posts) as add_posts,
  max(remove_posts) as remove_posts,
  max(modify_users) as modify_users,
  max(add_users) as add_users,
  max(delete_users) as delete_users
from
(
select 
  max(add_posts) as add_posts,
  max(remove_posts) as remove_posts,
  max(modify_users) as modify_users,
  max(add_users) as add_users,
  max(delete_users) as delete_users
from
  groups
where
  group_id in (select group_id from user_groups where user_id = 3)
union all
select  
  max(add_posts) as add_posts,
  max(remove_posts) as remove_posts,
  max(modify_users) as modify_users,
  max(add_users) as add_users,
  max(delete_users) as delete_users
from 
  user_rights
where
  user_id = 3
) as combined_user_groups

鉴于上述数据将为我在 WHERE 子句中指定的任何用户提供有效权限。我想要做的是创建一个物化视图，该视图仅在用户或组数据更改时更新，但在其他情况下是静态的。我知道如何毫无问题地做到这一点 - 我遇到的问题是生成此视图。我的想法是使用上面的查询 - 但让它为“users”表中的每个用户运行并创建一个“user_id”列。所以我的“有效权限”表将如下所示：

user_id, add_posts, remove_posts, modify_users, add_users, delete_users
1        1          1             1             1          1
2        1          1             1             1          1
3        0          0             1             1          1

..等等。我只是不知道如何将 user_id 添加到此结果并显示多行。我希望我已经提供了足够的信息，让人们能够理解我正在尝试做的事情。我意识到，一旦表按大小分组，最终这种方法在性能方面可能会变得相当昂贵 - 而这个解决方案似乎是我能想到的缓解该问题的最佳解决方案。

如果您想重新创建示例数据以进行测试，那么提供的示例应该可以工作（我刚刚在本地 pg 服务器上快速重建了它，尽管它比应用相同概念的真实表简单得多）。

Answer 1

select
  user_id
  max(add_posts) as add_posts,
  max(remove_posts) as remove_posts,
  max(modify_users) as modify_users,
  max(add_users) as add_users,
  max(delete_users) as delete_users
from
(
select 
  ug.user_id
  max(g.add_posts) as add_posts,
  max(g.remove_posts) as remove_posts,
  max(g.modify_users) as modify_users,
  max(g.add_users) as add_users,
  max(g.delete_users) as delete_users
from
  groups g
inner join
  users_groups ug
on g.group_id = ug.group_id
group by    
  ug.user_id
union
select
  user_id  
  max(add_posts) as add_posts,
  max(remove_posts) as remove_posts,
  max(modify_users) as modify_users,
  max(add_users) as add_users,
  max(delete_users) as delete_users
from 
  user_rights
group by
  user_id
) as combined_user_groups
group by
  user_id