Question

我使用这些查询来选择具有相似图书选择的用户的user_id。

SELECT r2.user_id
FROM `read` r1
JOIN `read` r2
ON r1.user_id <> r2.user_id AND r1.book_id = r2.book_id
WHERE r1.user_id = 1
GROUP BY r2.user_id
HAVING count(*) >= 5

但我不想只显示user_id。还有来自其他表的关于这个user_id的数据！

上面的查询仅使用此表：

CREATE TABLE `read` (
  `id` int(11) unsigned NOT NULL AUTO_INCREMENT,
  `user_id` int(11) unsigned NOT NULL,
  `book_id` int(11) unsigned NOT NULL,
  PRIMARY KEY (`id`),
  UNIQUE KEY `No duplicates` (`user_id`,`book_id`),
  KEY `book_id` (`book_id`),
  CONSTRAINT `connections_ibfk_1` FOREIGN KEY (`user_id`) REFERENCES `users` (`id`) ON DELETE CASCADE ON UPDATE CASCADE,
  CONSTRAINT `connections_ibfk_2` FOREIGN KEY (`book_id`) REFERENCES `books` (`id`) ON DELETE CASCADE ON UPDATE CASCADE
) ENGINE=InnoDB DEFAULT CHARSET=utf8;

但我也有：

CREATE TABLE `users` (
  `id` int(11) unsigned NOT NULL AUTO_INCREMENT,
  `email` char(255) NOT NULL DEFAULT '',
  `password` char(12) NOT NULL,
  PRIMARY KEY (`id`),
  UNIQUE KEY `email` (`email`)
) ENGINE=InnoDB AUTO_INCREMENT=3 DEFAULT CHARSET=utf8;

和

CREATE TABLE `books` (
  `id` int(11) unsigned NOT NULL AUTO_INCREMENT,
  `book` char(55) NOT NULL DEFAULT '',
  `user_id` int(11) unsigned NOT NULL,
  PRIMARY KEY (`id`),
  UNIQUE KEY `book` (`book`),
  KEY `user_id` (`user_id`),
  CONSTRAINT `books_ibfk_1` FOREIGN KEY (`user_id`) REFERENCES `users` (`id`) ON DELETE NO ACTION ON UPDATE CASCADE
) ENGINE=InnoDB DEFAULT CHARSET=utf8;

因此，对于我的查询生成的列表中的每个user_id，我还希望来自email的{{1}}。以及为该用户阅读的所有book_ids，但这些book_ids是ID，我希望它能够根据book_ids显示书籍。

哇，有人会理解我写的吗？

：L）

Answer 1

试试这个

    SELECT r2.user_id,u1.email,b1.books
    FROM `read` r1
    JOIN `read` r2
    ON r1.user_id <> r2.user_id AND r1.book_id = r2.book_id
    JOIN `users` u1
    ON r2.user_id =u1.id
    JOIN `books` b1
    ON r1.book_id=b1.id
    WHERE r1.user_id = 1
    GROUP BY r2.user_id
    HAVING count(*) >= 5

Answer 2

试试这个。希望没有语法错误。如果它不起作用，请转到SQLFiddle.com并加载一些测试数据

SELECT users.id, users.email, book.books
FROM (
  SELECT r2.user_id
  FROM `read` r1
  JOIN `read` r2
    ON r1.user_id <> r2.user_id 
      AND r1.book_id = r2.book_id
  WHERE r1.user_id = 1
  GROUP BY r2.user_id
  HAVING count(*) >= 5) as t1
 JOIN users
   ON t1.user_id = users.id
 JOIN read
   ON read.user_id = t1.user_id
 JOIN books
   ON books.id = read.book_id
 WHERE EXISTS(SELECT * 
              FROM read 
              WHERE read.user_id = 1 
                AND read.book_id = book.id)

总结一个列表 - 按照共同降序的书籍排序：

SELECT users.id, users.email, t1.qty, GROUP_CONCAT(book.books)
FROM (
  SELECT r2.user_id, COUNT(*) AS qty
  FROM `read` r1
  JOIN `read` r2
    ON r1.user_id <> r2.user_id 
      AND r1.book_id = r2.book_id
  WHERE r1.user_id = 1
  GROUP BY r2.user_id
  HAVING count(*) >= 5) as t1
 JOIN users
   ON t1.user_id = users.id
 JOIN read
   ON read.user_id = t1.user_id
 JOIN books
   ON books.id = read.book_id
 WHERE EXISTS(SELECT * 
              FROM read 
              WHERE read.user_id = 1 
                AND read.book_id = book.id)
 GROUP BY users.id, users.email, t1.qty
 ORDER BY t1.qty DESC, users.email ASC

从单个查询-mysql中的多个表中获取数据

2 个答案: