PHP，SQL新手帮助

我有下表：

Comments -------- id PK cid content uid comment 好了。$cid周围的花括号并不是严格意义上的nessecary，但它们有助于避免出现这样的问题：如果您试图在之后打印文本，它会将变量名作为其他内容读取

$q="SELECT c.id, c.cid, c.content, c.uid, c.comment,
    COALESCE(t.title,i.title) AS the_title
    FROM comments c LEFT JOIN threads t ON (c.cid=t.id AND c.content='thread')
                    LEFT JOIN images i ON (c.cid=i.id AND c.content='image');

---

上面将两个查询组合在一起，并将title属性放在一列中

@George Stocker:你的编辑使问题更难阅读。+1代表创造性的解决方案-1，因为它是罕见的（我第一次看到COALESCE），并且会混淆一个新站点。COALESCE获取其参数列表中的第一个非NULL值并输出它。如果您的查询中有几个字段是互斥的，或者需要按特定的优先顺序选择，那么它非常有用。

 while ($row = mysql_fetch_assoc($rs)) {
   if($row['content'] == "image") {
        echo "?imgID={$cid}";
        $title = mysql_fetch_assoc(mysql_query("SELECT title from images WHERE id = '$cid'");
   } elseif ($row['content'] == "thread") {
        echo "?threadID={$cid}";
        $title = $row['title']; // Will only work as long as there is no title field in comments, oherwise use threads.title
   }
 }
 echo $title;

$q="SELECT c.id, c.cid, c.content, c.uid, c.comment,
    COALESCE(t.title,i.title) AS the_title
    FROM comments c LEFT JOIN threads t ON (c.cid=t.id AND c.content='thread')
                    LEFT JOIN images i ON (c.cid=i.id AND c.content='image');