关于一个很菜的问题！！请大家帮助！！

[wangqiu]

select a,b,row_number() over(pratition by a order by b) rm from table

这里面的over和pratition by是什么意思？？？还有row_number()是什么？？

这句话什么意思？？？

[wangqiu]

怎么没人回答我的问题？？？

我菜，大家就不能帮帮我吗？？

[beckhambobo]

over是分析函数关键字，pratition by是分组意思

ROW_NUMBER is an analytic function. It assigns a unique number to each row to which it is applied (either each row in the partition or each row returned by the query), in the ordered sequence of rows specified in the ORDER_BY_clause, beginning with 1.

You cannot use ROW_NUMBER or any other analytic function for expr. That is, you can use other built-in function expressions for expr, but you cannot nest analytic functions.

See Also: "Expressions" for information on valid forms of expr




Example
For each department in the emp table, the following example assigns numbers to each row in order of employee's hire date:

SELECT deptno, ename, hiredate, ROW_NUMBER()
OVER (PARTITION BY deptno ORDER BY hiredate) AS emp_id
FROM emp;

DEPTNO ENAME HIREDATE EMP_ID
---------- ---------- --------- ----------
10 CLARK 09-JUN-81 1
10 KING 17-NOV-81 2
10 MILLER 23-JAN-82 3
20 SMITH 17-DEC-80 1
20 JONES 02-APR-81 2
20 FORD 03-DEC-81 3
20 SCOTT 19-APR-87 4
20 ADAMS 23-MAY-87 5
30 ALLEN 20-FEB-81 1
30 WARD 22-FEB-81 2
30 BLAKE 01-MAY-81 3
30 TURNER 08-SEP-81 4
30 MARTIN 28-SEP-81 5
30 JAMES 03-DEC-81 6

[wangqiu]

可以用汉语通俗的说一下吗？？我英语很差。