rank,dense_rank,row_number区别

一：语法(用法)：
     rank() over([partition by col1] order by col2) 
     dense_rank() over([partition by col1] order by col2) 
     row_number() over([partition by col1] order by col2) 
     其中[partition by col1]可省略。

二：区别
    三个分析函数都是按照col1分组内从1开始排序
    
    row_number() 是没有重复值的排序(即使两天记录相等也是不重复的)，可以利用它来实现分页
    dense_rank() 是连续排序，两个第二名仍然跟着第三名
    rank()       是跳跃拍学，两个第二名下来就是第四名
    
    理论就不多讲了，看了案例，一下就明白了
    
SQL> create table t(
  2   name varchar2(10),
  3   score number(3));
 
Table created
 
SQL> insert into t(name,score) 
  2   select '语文',60 from dual union all
  3   select '语文',90 from dual union all
  4   select '语文',80 from dual union all
  5   select '语文',80 from dual union all
  6   select '数学',67 from dual union all
  7   select '数学',77 from dual union all
  8   select '数学',78 from dual union all
  9   select '数学',88 from dual union all
 10   select '数学',99 from dual union all
 11   select '语文',70 from dual
 12  /
 
10 rows inserted
 
SQL> select * from t;
 
NAME       SCORE
---------- -----
语文          60
语文          90
语文          80
语文          80
数学          67
数学          77
数学          78
数学          88
数学          99
语文          70
 
10 rows selected
 
SQL> select name,score,rank() over(partition by name order by score) tt from t;
 
NAME       SCORE         TT
---------- ----- ----------
数学          67          1
数学          77          2
数学          78          3
数学          88          4
数学          99          5
语文          60          1
语文          70          2
语文          80          3   <----
语文          80          3   <----
语文          90          5
 
10 rows selected
 
SQL> select name,score,dense_rank() over(partition by name order by score) tt from t;
 
NAME       SCORE         TT
---------- ----- ----------
数学          67          1
数学          77          2
数学          78          3
数学          88          4
数学          99          5
语文          60          1
语文          70          2
语文          80          3   <----
语文          80          3   <----
语文          90          4
 
10 rows selected
 
SQL> select name,score,row_number() over(partition by name order by score) tt from t;
 
NAME       SCORE         TT
---------- ----- ----------
数学          67          1
数学          77          2
数学          78          3
数学          88          4
数学          99          5
语文          60          1
语文          70          2
语文          80          3  <----
语文          80          4  <----
语文          90          5
 
10 rows selected
 
SQL> select name,score,rank() over(order by score) tt from t;
 
NAME       SCORE         TT
---------- ----- ----------
语文          60          1
数学          67          2
语文          70          3
数学          77          4
数学          78          5
语文          80          6
语文          80          6
数学          88          8
语文          90          9
数学          99         10
 
10 rows selected

大家应该明白了吧！呵呵！接下来看应用

一：dense_rank------------------查询每门功课前三名

select name,score from (select name,score,dense_rank() over(partition by name order by score desc) tt from t) x where x.tt<=3
  
 
NAME       SCORE
---------- -----
数学          99
数学          88
数学          78
语文          90
语文          80
语文          80
 
6 rows selected

二:rank------------------语文成绩70分的同学是排名第几。
   select name,score,x.tt from (select name,score,rank() over(partition by name order by score desc) tt from t) x where x.name='语文' and x.score=70
 
 
NAME       SCORE         TT
---------- ----- ----------
语文          70          4
    
三：row_number——————分页查询
     select xx.* from (select t.*,row_number() over(order by score desc) rowno from t) xx where xx.rowno between 1 and 3;
 
NAME       SCORE      ROWNO
---------- ----- ----------
数学          99          1
语文          90          2
数学          88          3