学步园

oracle 分许函数 row_number(),返回一个整数值(>=1);

语法格式:

1.row_number() over (order by col_1[,col_2 ...])

作用:按照col_1[,col_2 ...]排序,返回排序后的结果集，

此用法有点像rownum,为每一行返回一个不相同的值：

select rownum,ename,job,<br /> row_number() over (order by rownum) row_number<br /> from emp;<br /> ROWNUM ENAME JOB ROW_NUMBER<br /> ---------- ---------- --------- ----------<br /> 1 SMITH CLERK 1<br /> 2 ALLEN SALESMAN 2<br /> 3 WARD SALESMAN 3<br /> 4 JONES MANAGER 4<br /> 5 MARTIN SALESMAN 5<br /> 6 BLAKE MANAGER 6<br /> 7 CLARK MANAGER 7<br /> 8 SCOTT ANALYST 8<br /> 9 KING PRESIDENT 9<br /> 10 TURNER SALESMAN 10<br /> 11 ADAMS CLERK 11<br /> 12 JAMES CLERK 12<br /> 13 FORD ANALYST 13<br /> 14 MILLER CLERK 14 

如果没有partition by子句, 结果集将是按照order by 指定的列进行排序；

with row_number_test as(<br /> select 22 a,'twenty two' b from dual union all<br /> select 1,'one' from dual union all<br /> select 13,'thirteen' from dual union all<br /> select 5,'five' from dual union all<br /> select 4,'four' from dual)<br /> select a,b,<br /> row_number() over (order by b)<br /> from row_number_test<br /> order by a; 

正如我们所期待的,row_number()返回按照b列排序的结果,

然后再按照a进行排序,才得到下面的结果:

A B ROW_NUMBER()OVER(ORDERBYB)<br /> ---------- ---------- --------------------------<br /> 1 one 3<br /> 4 four 2<br /> 5 five 1<br /> 13 thirteen 4<br /> 22 twenty two 5 

2.row_number() over (partition by col_n[,col_m ...] order by col_1[,col_2 ...])

作用:先按照col_n[,col_m ...进行分组,

再在每个分组中按照col_1[,col_2 ...]进行排序(升序),

最后返回排好序后的结果集:

with row_number_test as(<br /> select 22 a,'twenty two' b,'*' c from dual union all<br /> select 1,'one','+' from dual union all<br /> select 13,'thirteen','*' from dual union all<br /> select 5,'five','+' from dual union all<br /> select 4,'four','+' from dual)<br /> select a,b,<br /> row_number() over (partition by c order by b) row_number<br /> from row_number_test<br /> order by a; 

这个例子中，我们先按照c列分组，分为2组('*'组,'+'组)，

再按照每个小组的b列进行排序(按字符串首字母的ascii码排),

最后按照a列排序,得到下面的结果集:

A B ROW_NUMBER<br /> ---------- ---------- ----------<br /> 1 one 3<br /> 4 four 2<br /> 5 five 1<br /> 13 thirteen 1<br /> 22 twenty two 2 

原文：http://www.adp-gmbh.ch/ora/sql/analytical/row_number.html