select * from art left join user on art.uid=user.id where 查询条件(如:art.uid='".$id."')
$sql=select * from art left join user on art.uid=user.id where 查询条件
$q=mysql_query($sql);
$result=mysql_fetch_array($q);
$result是结果集,遍历出结果就行了
$result["name"]即为user的名字
select * from user where id= (select uid from art )