MySQL加入唯一

Question

我有两个表，我需要从（classifieds_items和附件）拉记录。分类项目的图像存储在不同的表格（附件）中，每个分类的图像可能有多个。我需要为每个分类项目拉一张图片。下面的声明的问题是它会复制结果与项目有多个图像。

$sql = "SELECT * 
      FROM classifieds_items 
      JOIN (attachments) ON (attachments.attach_rel_id = classifieds_items.item_id) 
     WHERE active = 1 
      AND open = 1 
      AND date_expiry > ". time()." 
      AND attachments.attach_rel_module = 'classifieds' 
     ORDER BY RAND() 
     LIMIT 4"; 

$rs = mysql_query($sql);  

if(mysql_num_rows($rs)>0) { 
    while($row=mysql_fetch_array($rs)) { 
    $dtl_list .="<div class='fclass'> 
       <span class='fctitle'><a class='albumlnk' href='#'>".stripslashes($row['name']). '</a></span><br /> 
       <img src="uploads/'.stripslashes($row['attach_thumb_location']).'" /><br /> 
       '.stripslashes($row['price'])." 
       </div>"; 
    } 
} 

echo $dtl_list; 

Answer 1

在MySQL中，你可以再补充GROUP BY classifieds_items.item_id：

`$sql = "SELECT * 
      FROM classifieds_items 
      JOIN (attachments) ON (attachments.attach_rel_id = classifieds_items.item_id) 
     WHERE active = 1 
      AND open = 1 
      AND date_expiry > ". time()." 
      AND attachments.attach_rel_module = 'classifieds' 
     GROUP BY classifieds_items.item_id 
     ORDER BY RAND() 
     LIMIT 4";`