Mysql 将3个表连接在一起

我需要从这3个表中检索数据

users
+----------+-----------+
| username | last_name |
+----------+-----------+
| name     | last name |
+----------+-----------+
messages
+----+---------+-----------+---------+------+---------------------+
| id | to_user | from_user | message | read | sent                |
+----+---------+-----------+---------+------+---------------------+
| 12 |      12 |        10 | 1       |    0 | 2012-01-10 17:06:14 |
+----+---------+-----------+---------+------+---------------------+
all_messages
+----+--------+--------+
| id | user_1 | user_2 |
+----+--------+--------+
|  1 |     10 |     12 |
+----+--------+--------+

我需要选择所有这些数据，但仅当用户_1等于随机数时 用户_2等于from_user，用户_2等于users.id现在如果只有两个表，我选择所需数据没有问题，但我不知道如何连接表3，表3是用户，我的当前查询不包括用户表：

SELECT `all_messages`.`user_1`, `messages`.*
FROM `all_messages`
JOIN `messages` 
ON (`all_messages`.`user_2` = `messages`.`from_user`) 
WHERE `all_messages`.`user_1` = '12'
ORDER BY `messages`.`id` DESC LIMIT 2

编辑谢谢你的回答它工作得很好

---

但是，如果我只需要从消息中获取最后一条记录，因为现在它获取所有记录，其中all_messages.user_2=messages.from_user，我只需要获取最后一条最新记录，你只需要添加一个新加入，如下所示：

SELECT `all_messages`.`user_1`, `messages`.*
FROM `all_messages`
JOIN `messages` ON (`all_messages`.`user_2` = `messages`.`from_user`) 
JOIN users      ON (...write your condition here...)
WHERE `all_messages`.`user_1` = '12'
ORDER BY `messages`.`id` DESC LIMIT 2

---

您只需添加一个新联接，如下所示：

SELECT `all_messages`.`user_1`, `messages`.*
FROM `all_messages`
JOIN `messages` ON (`all_messages`.`user_2` = `messages`.`from_user`) 
JOIN users      ON (...write your condition here...)
WHERE `all_messages`.`user_1` = '12'
ORDER BY `messages`.`id` DESC LIMIT 2

---

您只需使用第三个表向查询中添加另一个联接：

SELECT `all_messages`.`user_1`, `messages`.*
FROM `all_messages`
JOIN `messages` 
ON (`all_messages`.`user_2` = `messages`.`from_user`) 
JOIN  `users`
ON (`users`.`id` = `all_messages`.`user_2`)
WHERE `all_messages`.`user_1` = '12'
ORDER BY `messages`.`id` DESC LIMIT 2

---

您只需使用第三个表向查询中添加另一个联接：

SELECT `all_messages`.`user_1`, `messages`.*
FROM `all_messages`
JOIN `messages` 
ON (`all_messages`.`user_2` = `messages`.`from_user`) 
JOIN  `users`
ON (`users`.`id` = `all_messages`.`user_2`)
WHERE `all_messages`.`user_1` = '12'
ORDER BY `messages`.`id` DESC LIMIT 2

---

用户中是否有主列？用户中是否有主列？