已有数据库，替换一下取数据库的值

我从网上找到代码

<?php  
require_once '../../../init.php';
$per_page = 3;  
$sqlc = "show columns from content";  
$rsdc = mysql_query($sqlc);  
$cols = mysql_num_rows($rsdc);  
$page = $_REQUEST['page'];  
$start = ($page-1)*3;  
$sql = "select * from content order by id limit $start,3";  
$rsd = mysql_query($sql);  
?>  
<?php  
while ($rows = mysql_fetch_assoc($rsd))  
{?>  
    <div class="shopp">  
        <div class="label"><?php echo substr($rows['message'],0,150);?></div>  
    </div>  
<?php }?>  

我的程序数据库是这样链接的

global $userData;
$db = Database::getInstance();

我想取数据库内的这几个字段

"select id,content,img,author,type,create_time from a_weiyu limit $start,3"

content img author type create_time
请问怎么改动 数据库的表是a_weiyu