ROW_NUMBER() OVER()

ROW_NUMBER()OVER() 是oracle SQL分析函数，主要是用来对要查询的数据分组排序使用。
使用方法
ROW_NUMBER()OVER(PARTITION BY col1 ORDER BY col2）
对列col1分组，col2排序操作。
例子：

SQL> SELECT 
  2   ROW_NUMBER()OVER(PARTITION BY deptno ORDER BY sal, empno) AS rn,
  3   empno, ename, sal, deptno
  4  FROM emp;

    RN  EMPNO ENAME     SAL DEPTNO
---------- ---------- ---------- ---------- ----------
     1   7934 MILLER           1300     10
     2   7782 CLARK        2450     10
     3   7839 KING         5000     10
     1   7369 SMITH     800     20
     2   7876 ADAMS        1100     20
     3   7566 JONES        2975     20
     4   7788 SCOTT        3000     20
     5   7902 FORD         3000     20
     1   7900 JAMES     950     30
     2   7521 WARD         1250     30
     3   7654 MARTIN           1250     30

    RN  EMPNO ENAME     SAL DEPTNO
---------- ---------- ---------- ---------- ----------
     4   7844 TURNER           1500     30
     5   7499 ALLEN        1600     30
     6   7698 BLAKE        2850     30

14 rows selected.

同时也可以单独使用其来对结果进行排序
可以和order by 对比一下：

SQL> SELECT empno,ename,sal, 2 ROW_NUMBER()OVER(ORDER BY sal,empno) AS rn
 3 FROM emp;

 EMPNO ENAME SAL RN
---------- ---------- ---------- ----------
 7369 SMITH 800 1
 7900 JAMES 950 2
 7876 ADAMS 1100 3
 7521 WARD 1250 4
 7654 MARTIN 1250 5
 7934 MILLER 1300 6
 7844 TURNER 1500 7
 7499 ALLEN 1600 8
 7782 CLARK 2450 9
 7698 BLAKE 2850 10
 7566 JONES 2975 11

 EMPNO ENAME SAL RN
---------- ---------- ---------- ----------
 7788 SCOTT 3000 12
 7902 FORD 3000 13
 7839 KING 5000 14

14 rows selected.


Execution Plan ----------------------------------------------------------
Plan hash value: 3145491563

--------------------------------------------------------------------------- | Id | Operation | Name | Rows | Bytes | Cost (%CPU)| Time | ---------------------------------------------------------------------------
|   0 | SELECT STATEMENT   |      |    14 |   462 | 4  (25)| 00:00:01 |
|   1 |  WINDOW SORT       |      |    14 |   462 | 4  (25)| 00:00:01 |
| 2 | TABLE ACCESS FULL| EMP | 14 | 462 | 3 (0)| 00:00:01 | ---------------------------------------------------------------------------

Note -----
 - dynamic sampling used for this statement (level=2)


Statistics ----------------------------------------------------------
 5 recursive calls
 0 db block gets
 16 consistent gets
 1 physical reads
 0 redo size
 1049 bytes sent via SQL*Net to client
 523 bytes received via SQL*Net from client
 2 SQL*Net roundtrips to/from client
 1 sorts (memory)
 0 sorts (disk)
 14 rows processed

SQL> SELECT empno,sal
 2 FROM emp
 3 ORDER BY sal,empno;

 EMPNO ENAME SAL
---------- ---------- ----------
 7369 SMITH 800
 7900 JAMES 950
 7876 ADAMS 1100
 7521 WARD 1250
 7654 MARTIN 1250
 7934 MILLER 1300
 7844 TURNER 1500
 7499 ALLEN 1600
 7782 CLARK 2450
 7698 BLAKE 2850
 7566 JONES 2975

 EMPNO ENAME SAL
---------- ---------- ----------
 7788 SCOTT 3000
 7902 FORD 3000
 7839 KING 5000

14 rows selected.


Execution Plan ----------------------------------------------------------
Plan hash value: 150391907

--------------------------------------------------------------------------- | Id | Operation | Name | Rows | Bytes | Cost (%CPU)| Time | ---------------------------------------------------------------------------
|   0 | SELECT STATEMENT   |      |    14 |   462 | 4  (25)| 00:00:01 |
|   1 |  SORT ORDER BY     |      |    14 |   462 | 4  (25)| 00:00:01 |
| 2 | TABLE ACCESS FULL| EMP | 14 | 462 | 3 (0)| 00:00:01 | ---------------------------------------------------------------------------

Note -----
 - dynamic sampling used for this statement (level=2)


Statistics ----------------------------------------------------------
 4 recursive calls
 0 db block gets
 16 consistent gets
 1 physical reads
 0 redo size
 943 bytes sent via SQL*Net to client
 523 bytes received via SQL*Net from client
 2 SQL*Net roundtrips to/from client
 1 sorts (memory)
 0 sorts (disk)
 14 rows processed

对比ORDER BY 子句，排序结果一样，使用ROW_NUMBER()OVER()函数可生产RN列，便于在某些列表程序选择行数。

（编辑：李大同）

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