随机排序获取列表；

$sql="select * from article  order by dbms_random.value()";

获取指定条数的数据：

$sql="select * from article where rownum<=$limit";

$sql1="select *,rownum rn from article";

$sql1="select * from ($sql1)s where s.rn<=$limit";

分组计数：

select category,count(*) count from article group by category;

分页获取列表数据：

$start=($page-1)*$perpage+1;
$end=$perpage*$page;

$sql="select * from article";

$sql="SELECT * FROM
             ( 
                 select a.*,rownum row_num from($sql)a
             )b
WHERE b.row_num between $start and $end";