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;

mysql 实现row_number，获取上一条，下一条