如何查询一个用户所有好友的帖子（存储在3个MySQL表之间）？

Question

所以我有用户信息、用户发布的内容和朋友都在单独的 tables 中。

示例数据：

用户：

id    username      email
1     userA         myemail@testa.com
2     userB         myemail@testb.com
3     userC         myemail@testc.com

user_content

id    user_id      date                     text
1     1             2015-09-12 00:24:08     content here
2     2             2015-09-11 00:24:08     more content here a
3     1             2015-09-10 00:24:08     more content here b
4     3             2015-09-05 00:24:08     more content here c

朋友

id    user_id_1  user_id_2
1     1          2
2     2          3
3     2          4

user table 存储有关特定用户的信息，user_content 存储该用户发布的内容，friends 存储 'friend' 用户之间的关联。

我的问题是，我如何查询此数据以获得按日期排序的特定用户的所有朋友的 user_content？目前我遍历特定用户的每个朋友：

$stmt = $mysqli->prepare("SELECT user_id_1, user_id_2 FROM friends WHERE user_id_1 = ? OR user_id_2 = ?");
$stmt->bind_param("ii", $userID, $userID);
$stmt->execute();
$stmt->store_result();
$stmt->bind_result($db_user_id_1, $db_user_id_2);
while ($stmt->fetch()) {
    //Work out which is the user, and which is the friend
    $friendID = $db_user_id_1;
    if ($userID == $db_user_id_1) {
        $friendID = $db_user_id_2;
    }

    //Load latest 10 user_content for each user, store in memory and sort by date
}
$stmt->close();

但这在单个 MySQL 查询中可能吗？遍历每个朋友然后按日期排序的开销似乎有点过分了。我只想要特定用户的所有朋友的最新 30 user_content。

Answer 1

您需要的是 LEFT JOIN。

SELECT u.`username`, u.`email`, c.`text`, c.`date`
FROM user AS u
LEFT JOIN friends AS f ON f.`user_id_1` = u.`id`
LEFT JOIN user_content AS c ON c.`user_id` = f.`user_id_2`
WHERE u.`username` = 'userA'
ORDER BY c.`date` ASC
LIMIT 0,30

这将根据您的条件连接 table friends、user 和 user_content。

Answer 2

我没有完全理解你的目标。

但这是我获取某些 ? 用户朋友的所有内容的方法：

http://sqlfiddle.com/#!9/fb40e/2

SELECT uc.*
FROM user_content uc
INNER JOIN friends f
ON f.user_id_2 = uc.user_id
  AND f.user_id_1 = ?

UPDATE 如果您不确定哪个字段是 uder_id 哪个字段是 friend_id 您可以使用 OR 进行转换：

http://sqlfiddle.com/#!9/fb40e/3

SELECT uc.*
FROM user_content uc
INNER JOIN friends f
ON (f.user_id_2 = uc.user_id
  AND f.user_id_1 = ?)
  OR (f.user_id_1 = uc.user_id
  AND f.user_id_2 = ?)

Answer 3

Select from user_content inner joined on friends，抓取任何一个用户的所有内容，其中 user_content 记录不属于当前用户，但当前用户是其中之一朋友...或者只是看看查询

编辑： 忘记添加最后 30 个帖子的限制

SELECT
     uc.user_id AS friend_user_id
    ,u.username AS friend_username
    ,u.email AS friend_email
    ,uc.date
    ,uc.text
FROM user_content uc
INNER JOIN friends f ON uc.user_id IN (f.user_id_1,f.user_id_2)
INNER JOIN user u ON uc.user_id = u.id
WHERE uc.user_id != ? AND ? IN (f.user_id_1, f.user_id2)
ORDER BY date DESC
LIMIT 30;

如何查询一个用户所有好友的帖子（存储在3个MySQL表之间）？

How to query posts by all friends of a user (stored between 3 MySQL tables)?

php

mysql

mysqli

inner-join