mysql排序后序号的实现

mysql中排序后根据排序的内容显示序号，须要在子查询中select @rownum:=0，只有外层的@rownum并不会起做用。

select a.num, a.content, t.tagname,  @rownum:=@rownum+1 as sortorder from 
(select count(*) as num, content,  @rownum:=0 from action where actiontype='tag'
 group by content)a left join tag t on a.content=t.tagid 
order by a.num desc limit 10;

在没有子查询的状况下，能够在外面包一层查询。

SELECT n.*, @rownum:=@rownum+1 as sortorder from 
(SELECT COUNT(*) as num, vendor FROM  device WHERE LENGTH(vendor)>0 
GROUP BY vendor ORDER BY num DESC LIMIT 10) n, 
(SELECT @rownum := 0) r;