代码思路如下：
select *,(@row_num:=@row_num+1) as row_no from stc_output,(select(@row_num:=0)) b;
select * from (select *,(@row_num:=@row_num+1) as row_no from stc_output,(select(@row_num:=0)) b) a where a.row_no=2;
原文：http://www.cnblogs.com/beyond1983/p/3951994.html