开窗函数、高级排序函数：ROW_NUMBER()，RANK() ， DENSE_RANK ，OVER (partition by xx order by xx)，

开窗函数、高级排序函数：ROW_NUMBER()，RANK() ， DENSE_RANK ，OVER (partition by xx order by xx)，

高级排序函数: 
[ ROW_NUMBER()| RANK() | DENSE_RANK ] OVER (partition by xx order by xx)


1.row_number() 连续且递增的数字 1 2 3 4 
  row_number() over (partition by xx order by xx )  
  
--学生表中按照所在专业分组，同专业内按成绩倒序排序，成绩相同则按学号正序排序，并给予组内等级
select row_number() over(partition by class_id order by score desc)rn,t.* from student2016 t
  
2.rank() 跳跃排序 若有相同数据则排名相同 然后跳跃排序 1 2 2 2 5
  rank() over (partition by xx order by xx ) 


select rank() over(partition by class_id order by score desc)rn,t.* from student2016 t
  
3.dense_rank 若有相同数据则排名相同 然后递增排序
dense_rank  over (partition by xx order by xx ) 1 2 2 2 3


select dense_rank() over(partition by class_id order by score desc)rn,t.* from student2016 t