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)

select deptid,salary, row_number() OVER (PARTITION BY deptid ORDER BY salary) from employee

数据显示为:

"DEPTID"    ,"SALARY",        "ROW_NUMBER()OVER(PARTITIONBYDE"
"10",          "4500.00",                                  "1"
"10",          "5500.00",                                  "2"
"20",         "1900.00",                                   "1"
"20",         "4800.00",                                   "2"
"40",          "6500.00",                                  "1"
"40",          "14500.00",                                "2"
"40",         "44500.00",                                 "3"
"50",          "6500.00",                                  "1"
"50",          "7500.00",                                  "2"