使用两个内加入MySQL查询

Question

我有两个表像下面的图片：

用户表：

offer_comments

offer_comments表存储的意见和答案发表评论。 使用以下功能我可以根据$id得到评论和回答评论。

function getCommentsAnItem($id){ 

    mysql_query("SET CHARACTER SET utf8"); 
    $result_comments = mysql_query("select e.comment as comment,m.comment as answer_to_comment 
    from offer_comments e 
    inner join offer_comments m on e.id = m.quet 
    where e.offer_id=$id and e.confirm=1"); 
    $comments = array(); 
    while($a_comment=mysql_fetch_object($result_comments)){ 

     $comment = array(
     'comment'=>$a_comment->comment, 
     'answer'=>$a_comment->answer_to_comment 
     ); 
     array_push($comments,$comment); 
    } 

    return $comments ; 
} 

现在，我想用inner join代替offer_comments，我该怎么办？ 我想改用的offer_comments下面的SQL：

select offer.*,u.id,u.name,u.family from offer_comments offer 
     inner join users u on offer.id=u.id 

，如：

$result_comments = mysql_query("select e.comment as comment,m.comment as answer_to_comment 
    from (select offer.*,u.name,u.family from offer_comments offer 
    inner join users u on offer.id=u.id) e 
    inner join offer_comments m on e.id = m.quet 
    where e.offer_id=$id and e.confirm=1"); 

但它返回[]！

Answer 1

试试这个：

$result_comments = mysql_query("select e.comment as comment,m.comment as answer_to_comment 
    from (select offer.*,u.name,u.family from offer_comments offer 
    inner join users u on offer.user_id=u.id) e 
    inner join offer_comments m on e.id = m.quet 
    where e.offer_id=$id and e.confirm=1"); 

这里的变化是e派生表users和offer_comments之间的关系应该是users.id = offer_comments.user_id，你已经做到了users.id = offer_comments.id