row_number() OVER (PARTITION BY COL1 ORDER BY COL2)

--表示根据COL1分组，在分组内部根据 COL2排序，而此函数返回的值就表示每组内部排序后的顺序编号（组内连续的唯一的)

create table student (id int ,classes int ,score int);
insert into student values(1,1,89);
insert into student values(2,1,90);
insert into student values(3,1,76);
insert into student values(4,2,69);
insert into student values(5,2,79);
insert into student values(6,2,95);
insert into student values(7,3,80);
insert into student values(8,3,85);
insert into student values(9,3,79);
commit;

select t.* from student t;

--数据显示为

id       classes      score

-------------------------------------------------------------

1           1          89

2           1          90

3           1          76

4           2          69

5           2          79

6           2          95

7           3          80

8           3          85

9           3          79

--需求：根据班级分组，显示每个班的英语成绩排名

--预期结果：

id       classes      score                              rank

----------- ----------- ---------------------------------------

3           1          76                                 1

1           1          89                                 2

2           1          90                                 3

4           2          69                                 1

5           2          79                                 2

6           2          95                                 3

9           3          79                                 1

7           3          80                                 2

8           3          85                                 3

--SQL脚本：

SELECT *, Row_Number() OVER (partition by classes ORDER BY score desc) rank FROM student;

--查询t_test表中，callid字段没有重复过的数据，效率高过group by having count

select t.*, t.rowid
  from t_test t
 where t.rowid not in (select rid
                         from (select t2.rowid rid,
                                      row_number() over(partition by t2.callid order by t2.rowid desc) m
                                 from t_test t2)
                        where m <> 1)
   and t.rowid not in (select rid
                         from (select t2.rowid rid,
                                      row_number() over(partition by t2.callid order by t2.rowid asc) m
                                 from t_test t2)
                        where m <> 1);

row_number() OVER (PARTITION BY COL1 ORDER BY COL2)