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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 会抛出一个错误，因此虽然我的 SQL 在我看来在逻辑上有些合理 - 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是某种“物化视图”）。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);

我想要做的是创建一个可以计算用户可能拥有的有效权限的查询。用户存储在（您猜对了）“用户”表中。“groups”中的组，用户可能被分配到的任何组都在“user_groups”中。最后，每个用户都可以拥有应该覆盖组权限的个人权限 - 这些权限存储在“user_rights”中。

我可以使用以下方法查询所有这些信息（是的，我知道这很丑）：

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，我将为我在 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，但在其他方面是静态的。这我知道怎么做没有问题 - 我遇到的问题是生成这个视图。我的想法是使用上面的查询 - 但让它为“用户”表中的每个用户运行并创建一个“用户 ID”列。所以我的“effective_permissions”表看起来像这样：

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。我希望我已经为某人提供了足够的信息来了解我正在尝试做什么。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——而且这个解决方案似乎是我能想出的最好的解决方案来缓解这个问题。

如果您想为测试目的重新创建示例数据，则提供的示例应该可以工作（我只是在我的本地 pg 服务器上快速重建它，尽管它比相同概念适用的真实表要简单得多）。

4

1 回答 1

2 
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
于 2011-05-22T03:02:14.977 回答