从不在另一个表MySQL中的一个表中获取所有数据

时间：2018-11-15 02:26:00

标签： php mysql left-join having-clause

我有一个消息表：

  mysql> describe messages;
+-----------+--------------+------+-----+-------------------+-----------------------------+
| Field     | Type         | Null | Key | Default           | Extra                       |
+-----------+--------------+------+-----+-------------------+-----------------------------+
| id        | int(11)      | NO   | PRI | NULL              | auto_increment              |
| user1_id  | int(11)      | NO   |     | NULL              |                             |
| user1     | varchar(255) | NO   |     | NULL              |                             |
| user2_id  | int(11)      | NO   |     | NULL              |                             |
| user2     | varchar(255) | NO   |     | NULL              |                             |
| message   | text         | YES  |     | NULL              |                             |
| timestamp | timestamp    | NO   |     | CURRENT_TIMESTAMP | on update CURRENT_TIMESTAMP |
| user1read | varchar(3)   | NO   |     | NULL              |                             |
| user2read | varchar(3)   | NO   |     | NULL              |                             |
+-----------+--------------+------+-----+-------------------+-----------------------------+
9 rows in set (0.00 sec)

然后我有一个被阻止的表：

 mysql> describe blocked;
+-----------------+---------+------+-----+---------+-------+
| Field           | Type    | Null | Key | Default | Extra |
+-----------------+---------+------+-----+---------+-------+
| user_id         | int(11) | NO   | PRI | NULL    |       |
| blocked_user_id | int(11) | NO   | PRI | NULL    |       |
+-----------------+---------+------+-----+---------+-------+
2 rows in set (0.00 sec)

我想做的是获取所有数据以在页面上的单独div中显示。每秒调用一次此脚本。无论阻塞状态如何，我最终得到的查询都会产生所有消息。

因此，假设我的ID为1，被阻止的用户ID为5，则用户5不应显示在列表中。如果其他用户登录，则同样如此。

弄乱了该查询一段时间后，我尝试了第二次查询。甚至更糟，因为尽管使用相同的查询通过手动SQL条目返回了数据，但页面上却没有没有显示。

文件很小，所以我将发布整个内容：

编辑：第一个查询实际上是显示所有消息，包括我本人作为消息，这显然是错误的。看来我的查询比我想象的要难得多。

 <?php
session_start();

include '../../../config/DB.php';

$username = $_SESSION['logged_in']; //to use in queries

try {
    $db = new DB(); //new DB object
} catch (Exception $e) {
    $e->getMessage();
}

try {
    $names = array(); //to store during foreach iterations

    //get the id for the other query attempt
    $id_result = $db->getRow('SELECT id FROM users WHERE username=?', [$username]);
    $id = $id_result['id'];

    foreach ($messages_result = $db->getRows('SELECT messages.user1, messages.user2, messages.timestamp, messages.message, messages.user2read, users.avatar
                                                    FROM messages
                                                    LEFT JOIN users ON messages.user1 = users.username
                                                    WHERE messages.user2 = ? AND 
                                                    (users.id NOT IN (SELECT user_id FROM blocked))
                                                    OR (users.id NOT IN (SELECT blocked_user_id FROM blocked))
                                                    ORDER BY timestamp DESC', [$username]) as $result) {
        $sender = $result['user1'];
        $time = $result['timestamp'];
        $message = $result['message'];
        $avatar = $result['avatar'];
        $user2read = $result['user2read'];

        //Do this so users will only show once.
        //One div per user, and when clicked
        //all messages are shown elsewhere on a page.
        if (!in_array($sender, $names)) {
            $names[] = $sender;

            //If the message is unread, show name in bold
            //Else show regular text
            //$avatar has been removed from the html for now
            //It shows up in an <img> tag
            if ($user2read === 'no') {
                echo '<div id="single_message" data-sender="' . $sender . '"><p style="padding-left:8px;"><p><a class="link" style="font-weight:bold;font-size:16px;" href=' . $sender . '>' . $sender . '</a></strong></p><p style="white-space:pre-wrap;margin-left:8px;margin-right:8px;">' . $message . '</p><p style="padding-left:8px;border-bottom: 1px solid #ccc;">' . $time . '</p></div>';
            } else {
                echo '<div id="single_message" data-sender="' . $sender . '"><p style="padding-left:8px;"><p><a class="link" href=' . $sender . '>' . $sender . '</a></p><p style="white-space:pre-wrap;margin-left:8px;margin-right:8px;">' . $message . '</p><p style="padding-left:8px;border-bottom: 1px solid #ccc;">' . $time . '</p></div>';
            }

        } else {
            continue;
        }
    }

} catch (Exception $e) {
}

这是我尝试的第二个查询（我只会显示foreach）。这是在页面上什么都不显示的页面。

 foreach($messages_result = $db->getRows('SELECT * FROM messages m LEFT JOIN blocked b ON ((m.user1_id = b.user_id OR m.user2_id = b.user_id)
                                                    AND (m.user1_id = b.blocked_user_id OR m.user2_id = b.blocked_user_id))
                                                    WHERE (m.user1_id = 1 OR m.user2_id = 1) HAVING m.user_id IS NULL
                                                    ORDER BY timestamp DESC', [$id]) as $result) {

我在这里错过了什么吗？

3 个答案:

答案 0 :(得分：0)

WHERE (m.user1_id = 1 OR m.user2_id = 1) HAVING m.user_id IS NULL我认为它彼此矛盾，因为您在加入ON ((m.user1_id = b.user_id OR m.user2_id = b.user_id) AND (m.user1_id = b.blocked_user_id OR m.user2_id = b.blocked_user_id))时遇到这个问题。...就像互相抵消........

证明这一点。...也许可以...。祝你好运

答案 1 :(得分：0)

被阻止用户的左联接，其中user2（“我”）与被阻止者blocked.user_id和user1相对于blocked.blocked_user_id用户相匹配阻止，如果结果为NULL（又名b.user_id IS NULL），则没有阻止。

foreach($messages_result = $db->getRows('
SELECT messages.user1, messages.user2, messages.timestamp, messages.message, messages.user2read, users.avatar
FROM messages
LEFT JOIN users ON messages.user1 = users.username
LEFT JOIN blocked b ON b.user_id = messages.user2_id AND b.blocked_user_id = messages.user1_id
WHERE messages.user2 = ? AND b.user_id IS NULL
ORDER BY timestamp DESC',[$username]) as $result) {
...

答案 2 :(得分：0)

我有一个类似的脚本，它可以从用户表中获取所有未被阻止的用户，而不是从消息表中获取数据。由于此操作仅将用户ID与阻止的ID进行了比较，因此我可以使用一个查询块进行操作。但是，我需要从消息中检查user1_id和user2_id之间的所有可能性，并从阻止中检查user_id和blocked_user_id之间的所有可能性。这需要一个附加的块，它是第一个块的反向版本。

我将通过显示用户的ID和用户名，然后显示阻止表中的每个人的ID和用户名，然后使用阻止表中的ID来显示结果，以说明这是如何成功的。 

mysql> select id, username from users;
+----+-----------------+
| id | username        |
+----+-----------------+
|  1 | csheridan       |
|  2 | testuser        |
|  3 | testuser2       |
|  4 | washington_user |
+----+-----------------+
4 rows in set (0.00 sec)

mysql> select * from blocked;
+---------+-----------------+
| user_id | blocked_user_id |
+---------+-----------------+
|       1 |               2 |
|       1 |               4 |
+---------+-----------------+
2 rows in set (0.00 sec)

mysql> SELECT m.* FROM messages m   
       WHERE NOT EXISTS (SELECT 1 FROM blocked b 
       WHERE b.user_id = m.user1_id AND b.blocked_user_id = 1) 
       AND NOT EXISTS 
       (SELECT 1 FROM blocked b WHERE b.blocked_user_id = m.user1_id AND b.user_id = 1)   
       AND NOT EXISTS (SELECT 1 FROM blocked b WHERE b.user_id = m.user2_id AND b.blocked_user_id = 1) 
       AND NOT EXISTS (SELECT 1 FROM blocked b WHERE b.blocked_user_id = m.user2_id AND b.user_id = 1) 
       ORDER BY timestamp DESC;
+----+----------+-----------+----------+-----------+----------------+---------------------+-----------+-----------+
| id | user1_id | user1     | user2_id | user2     | message        | timestamp           | user1read | user2read |
+----+----------+-----------+----------+-----------+----------------+---------------------+-----------+-----------+
|  2 |        3 | testuser2 |        1 | csheridan | Hey!           | 2018-11-14 12:12:35 | yes       | no        |
|  4 |        3 | testuser2 |        1 | csheridan | Are you there? | 2018-11-14 12:12:35 | yes       | no        |
+----+----------+-----------+----------+-----------+----------------+---------------------+-----------+-----------+
2 rows in set (0.00 sec)

mysql> SELECT m.* FROM messages m   
       WHERE NOT EXISTS (SELECT 1 FROM blocked b  
       WHERE b.user_id = m.user1_id AND b.blocked_user_id = 2) 
       AND NOT EXISTS (SELECT 1 FROM blocked b WHERE b.blocked_user_id = m.user1_id AND b.user_id = 2)   
       AND NOT EXISTS (SELECT 1 FROM blocked b WHERE b.user_id = m.user2_id AND b.blocked_user_id = 2) 
       AND NOT EXISTS (SELECT 1 FROM blocked b WHERE b.blocked_user_id = m.user2_id AND b.user_id = 2) 
       ORDER BY timestamp DESC;
+----+----------+-----------------+----------+----------+---------------------+---------------------+-----------+-----------+
| id | user1_id | user1           | user2_id | user2    | message             | timestamp           | user1read | user2read |
+----+----------+-----------------+----------+----------+---------------------+---------------------+-----------+-----------+
|  7 |        4 | washington_user |        2 | testuser | Hey man! What's up? | 2018-11-14 14:32:27 | yes       | no        |
|  8 |        4 | washington_user |        2 | testuser | Hello there.        | 2018-11-14 14:32:27 | yes       | no        |
+----+----------+-----------------+----------+----------+---------------------+---------------------+-----------+-----------+
2 rows in set (0.00 sec)

所以，问题是我走在正确的轨道上，我只需要再下一块。首先，我检查blocked.user_id = messages.user1_id和blocked.user_id =？，然后检查user2_id的 other 条件。除非有人提出更紧凑的查询，否则这就是我所需要的。 如果我只执行第一个阻止，则它不会检查所有条件，并且仍会返回阻止的用户，因为它既未检查消息中的user1_id，也未同时检查user2_id。

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