sql 序号生成方法

 rank() 与dense_rank()分析 

1.rank()分析函数

语法:
RANK() OVER([PARTITION BY expr1[,expr2,..,exprn]] ORDER BY expr1[,expr2,..,exprn])

   功能:                                                                                                                                            先将记录按PARTITION分组,组内再以ORDER BY排序,算出当前记录在组内所处的级别(名次). PRATITION条件省略时,表明不分组,或将全录记录作为一组

例子: 有表如下:

SQL> select * from test;

NAME       SUBJECT         SCORE
---------- ---------- ----------
aa         chinese            90
aa         art                     88
aa         english            80
bb         chinese            80
bb         art                     92
bb         english            96
cc         chinese            73
cc         art                      78
cc         english            60

已选择9行。

执行语句如下:

SQL> break on name skip 1;
SQL> select * from ( select name ,subject,score ,rank() over ( partition byname order by score desc)
 score_rank  from  test)  where score_rank<=3;

NAME       SUBJECT         SCORE SCORE_RANK
---------- ---------- ---------- ----------
aa         chinese            90          1
                 art                88          2
           english            80          3

bb         english            96          1
                 art                92          2
           chinese            80          3

cc            art                78          1
           chinese            73          2
           english            60          3

已选择9行。

 

SQL> select * from (select name ,subject,score ,rank() over ( partition bysubject order by score desc) score_rank from test) where score_rank<=3;

NAME       SUBJECT         SCORE SCORE_RANK
---------- ---------- ---------- ----------
bb         art                92          1
aa                            88          2
cc                            78          3

aa         chinese     90          1
bb                            80          2
cc                            73          3

bb         english     96          1
aa                            80          2
cc                            60          3

已选择9行。

2.dense_rank函数

DENSE_RANK分析函数

语法:DENSE_RANK() OVER([PARTITION BY expr1[,expr2,..,exprn]] ORDER BY expr1[,expr2,..,exprn])

 

SQL> insert into test values('dd','chinese',80);

已创建 1 行。

SQL> insert into test values('dd','art',78);

已创建 1 行。

SQL> insert into test values('dd','english',96);

已创建 1 行。

SQL> select * from (select name ,subject,score,dense_rank() over ( partition bysubject order by score desc) score_rank from test) where score_rank<=3;

NAME       SUBJECT         SCORE SCORE_RANK
---------- ---------- ---------- ----------
dd         art                96          1
bb                            92          2
aa                            88          3
aa         chinese            90          1
bb                            80          2
cc                            73          3
bb         english            96          1
aa                            80          2
cc                            60          3

已选择9行。

SQL>  select * from (select name ,subject,score ,dense_rank() over ( partition byname order by score desc) score_rank from test) where score_rank<=3;

NAME       SUBJECT         SCORE SCORE_RANK
---------- ---------- ---------- ----------
aa         chinese            90          1
aa         art                     88          2
aa         english            80          3
bb                                 96          1
bb         art                    92          2
bb         chinese            80          3
cc         art                     78          1
cc         chinese            73          2
cc         english            60          3
dd         art                   96          1
dd                               80          2
dd                               78          3

已选择12行。

SQL> select * from (select name ,subject,score,rank() over ( partition byname order by score desc)
score_rank from test) where score_rank<=3;

NAME       SUBJECT         SCORE SCORE_RANK
---------- ---------- ---------- ----------
aa         chinese            90          1
aa         art                     88          2
aa         english            80          3
bb                                  96          1
bb         art                      92          2
bb         chinese            80          3
cc         art                      78          1
cc         chinese            73          2
cc         english            60          3
dd         art                96          1
dd                            80          2
dd                            78          3

已选择12行。

SQL> select * from (select name ,subject,score,rank()over ( partition by subject order by score desc) score_rank from test) where score_rank<=3;

NAME       SUBJECT         SCORE SCORE_RANK
---------- ---------- ---------- ----------
dd         art                96          1
bb                            92          2
aa                            88          3
aa         chinese      90          1
bb                            80          2
cc                            73          3
bb         english       96          1
aa                            80          2
cc                            60          3

已选择9行。

 

3.ROW_NUMBER() OVER函数的基本用法

语法：ROW_NUMBER() OVER(PARTITION BY COLUMN ORDER BY COLUMN)

简单的说row_number()从1开始，为每一条分组记录返回一个数字，这里的ROW_NUMBER() OVER (ORDER BY xlh DESC) 是先把xlh列降序，再为降序以后的没条xlh记录返回一个序号。
示例：
xlh           row_num
1700              1
1500              2
1085              3
710                4

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，而此函数计算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)

实例：

初始化数据

create table employee (empid int ,deptid int ,salary decimal(10,2))
insert into employee values(1,10,5500.00)
insert into employee values(2,10,4500.00)
insert into employee values(3,20,1900.00)
insert into employee values(4,20,4800.00)
insert into employee values(5,40,6500.00)
insert into employee values(6,40,14500.00)
insert into employee values(7,40,44500.00)
insert into employee values(8,50,6500.00)
insert into employee values(9,50,7500.00)

数据显示为

empid       deptid      salary
----------- ----------- ---------------------------------------
1           10          5500.00
2           10          4500.00
3           20          1900.00
4           20          4800.00
5           40          6500.00
6           40          14500.00
7           40          44500.00
8           50          6500.00
9           50          7500.00

需求：根据部门分组，显示每个部门的工资等级

预期结果：

empid       deptid      salary                                  rank
----------- ----------- --------------------------------------- --------------------
1           10          5500.00                                 1
2           10          4500.00                                 2
4           20          4800.00                                 1
3           20          1900.00                                 2
7           40          44500.00                               1
6           40          14500.00                               2
5           40          6500.00                                 3
9           50          7500.00                                 1
8           50          6500.00                                 2

SQL脚本：

SELECT *, Row_Number() OVER (partition by deptid ORDER BY salary desc) rank FROM employee