Question

我需要一些SQL查询的帮助。因为我是这个领域的新手，我无法真正解释谷歌我想做什么，我还没有找到任何正确的答案。我的桌子甚至可以吗？

我想收到所有的线程（id，name），这些线程不是我自己的线程，而且我已经没有投票了。（即线程我可以投票）

数据库如下所示：

Threads
+----+-------------+---------+
| id | thread_name | user_id |
+----+-------------+---------+
|  1 | Soccer      |       1 |
|  2 | Running     |       1 |
|  3 | Swimming    |       2 |
+----+-------------+---------+

User
+----+--------+
| id |  name  |
+----+--------+
|  1 | Marcel |
|  2 | Marc   |
|  3 | Susy   |
+----+--------+

Votes
+----+-----------+---------+
| id | thread_id | user_id |
+----+-----------+---------+
|  1 |         1 |       3 |
|  2 |         1 |       2 |
|  3 |         2 |       3 |
+----+-----------+---------+

示例：

如果用户1进行查询，他应该收到第3个帖子，因为它不是他自己的，他还没有投票。
用户2应该收到第2个帖子
用户4应该收到所有帖子

我试过了：

SELECT DISTINCT t.id, name FROM threads as t
LEFT JOIN votes as v ON v.thread_id = t.id
WHERE (v.user_id != USER_ID OR v.user_id IS NULL)
AND t.user_id != USER_ID

我正在使用Sequelize（Node.js ORM）。 pgAdmin给了我以下（简化）作为模式 - 希望这有帮助：

-- Table: "threads"
-- DROP TABLE "threads";

CREATE TABLE "threads"
(
  id serial NOT NULL,
  name character varying(255),
  "createdAt" timestamp with time zone NOT NULL,
  "updatedAt" timestamp with time zone NOT NULL,
  "user_id" integer,
  CONSTRAINT "threads_pkey" PRIMARY KEY (id),
  CONSTRAINT "threads_user_id_fkey" FOREIGN KEY ("user_id")
      REFERENCES "users" (id) MATCH SIMPLE
      ON UPDATE CASCADE ON DELETE SET NULL
)
WITH (
  OIDS=FALSE
);
ALTER TABLE "threads"
  OWNER TO postgres;

-- Table: "votes"
-- DROP TABLE "votes";

CREATE TABLE "votes"
(
  id serial NOT NULL,
  "createdAt" timestamp with time zone NOT NULL,
  "updatedAt" timestamp with time zone NOT NULL,
  "user_id" integer,
  "thread_id" integer,
  CONSTRAINT "votes_pkey" PRIMARY KEY (id),
  CONSTRAINT "votes_thread_id_fkey" FOREIGN KEY ("thread_id")
      REFERENCES "threads" (id) MATCH SIMPLE
      ON UPDATE CASCADE ON DELETE SET NULL,
  CONSTRAINT "votes_user_id_fkey" FOREIGN KEY ("user_id")
      REFERENCES "users" (id) MATCH SIMPLE
      ON UPDATE CASCADE ON DELETE SET NULL
)
WITH (
  OIDS=FALSE
);
ALTER TABLE "votes"
  OWNER TO postgres;


-- Table: "users"
-- DROP TABLE "users";

CREATE TABLE "users"
(
  id serial NOT NULL,
  username character varying(255),
  "createdAt" timestamp with time zone NOT NULL,
  "updatedAt" timestamp with time zone NOT NULL,
   CONSTRAINT "users_pkey" PRIMARY KEY (id)
)
WITH (
  OIDS=FALSE
);
   ALTER TABLE "users"
      OWNER TO postgres;

谢谢。

Answer 1

这应该可以解决您的问题。

select t.id from threads as t where t.user_id != USER_ID and t.id not in 
(select v.thread_id from votes as v where v.user_id = USER_ID);

“否定”SQL（postgres）查询

1 个答案: