一、檢查硬件

Oracle 分析函數(shù) row_number(),返回一個整數(shù)值(>=1);

語法格式:

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

作用:按照col_1[,col_2 ...]排序,返回排序后的結(jié)果集，

此用法有點(diǎn)像rownum,為每一行返回一個不相同的值：

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

如果沒有partition by子句, 結(jié)果集將是按照order by 指定的列進(jìn)行排序；

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

正如我們所期待的,row_number()返回按照b列排序的結(jié)果,

然后再按照a進(jìn)行排序,才得到下面的結(jié)果:

 A B          ROW_NUMBER()OVER(ORDERBYB)   
-- ---------- --------------------------   
 1 one                                 3   
 4 four                                2   
 5 five                                1   
13 thirteen                            4   
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 ...進(jìn)行分組,

再在每個分組中按照col_1[,col_2 ...]進(jìn)行排序(升序),

最后返回排好序后的結(jié)果集:

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

這個例子中，我們先按照c列分組，分為2組('*'組,'+'組)，

再按照每個小組的b列進(jìn)行排序(按字符串首字母的ascii碼排),

最后按照a列排序,得到下面的結(jié)果集:

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

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