获取行号

MySQL

select @rownum:=@rownum+1 rownum, seq_id from 
(  select @rownum:=0, seq_id from seq order by seq_id desc limit 20) t;

参考：
  [url]http://www.cnblogs.com/advocate/archive/2012/03/02/2376900.html [/url]
  http://blog.csdn.net/ACMAIN_CHM/article/details/4095531

Oracle
  rownum

SQL Server
  row_number()