一次从两个表中选择多个值

Question

代码

目前我的代码是这样的。

            $stmt = $this->db->prepare("SELECT m.id, m.from_id, m.to_id, m.subject, m.date, m.deleted, m.read, u.fname, u.mname, u.lname FROM msghistory AS m,users AS u WHERE m.from_id=u.id AND m.to_id=u.id AND GROUP BY m.id DESC");
            $stmt->execute();
            $stmt->store_result();
            if ($stmt->affected_rows > 0) {
                $msg = array();
                $stmt->bind_result($msg['id'], $msg['from_name'], $msg['to_name'], $msg['subject'], $msg['message'], $msg['date'], $msg['deleted'], $msg['read']);

                while ($stmt->fetch()) {
                    <echoing results one by one>                    }
            }

我想做什么

我想将u.fname+u.mname+u.lname（msghistory.from_id=users.id）作为$msg['from_name']，再次将u.fname+u.mname+u.lname（但是这次msghistory.to_id=users.id）作为$msg['to_name']。

示例

message | from_id | to-id
hi      | 1       | 5

如您所见，这意味着用户 1 向用户 5 发送消息 hi。

假设在用户表 fname 中，用户 id=1 的 lname - John Doe 和 5 - George Smith 我想将其显示为输出结果

message | from_id | to-id
hi      | John Doe| George Smith

问题

我知道至少有 3 个查询是可能的。但试图找到最佳方式。那么，这可以通过一个且唯一的查询来实现吗？

更新

根据用户的 2 个有用的答案，我将查询修改为此

            $stmt = $this->db->prepare("SELECT 
                message.id, message.from_id, message.to_id, message.subject, 
                message.date, message.deleted, message.read, 
                CONCAT_WS(' ',sender.fname, sender.mname, sender.lname) AS sender_name, 
                CONCAT_WS(' ',recipient.fname, recipient.mname, recipient.lname) AS recipient_name,  
                FROM msghistory AS message 
                LEFT JOIN users AS sender ON sender.id=message.from_id, 
                LEFT JOIN users AS recipient ON recipient.id=message.to_id 
                GROUP BY message.id DESC");

Answer 1

SELECT m.id, m.from_id, m.to_id, m.subject, m.date, 
m.deleted, m.read, u1.fname, u1.mname, u1.lname, 
u2.fname, u2.mname, u2.lname,       
FROM msghistory AS m,users AS u1, users As u2     
WHERE m.from_id=u1.id AND m.to_id=u2.id 
GROUP BY m.id DESC

我不确定您是否需要“分组依据”

Answer 2

使用显式连接和清晰易读的别名使其成为更健壮的查询并且更易于阅读。请尝试以下操作：

SELECT message.*, recipient.*, sender.*
FROM msghistory AS message
INNER JOIN users AS recipient ON recipient.id=m.to_id
INNER JOIN users AS sender ON sender.id=m.from_id

您可以将 select *s 替换为您想要提高效率的字段