sql over的作用及用法
RANK ( ) OVER ( [query_partition_clause] order_by_clause )
DENSE_RANK ( ) OVER ( [query_partition_clause] order_by_clause )
可實現按指定的字段分組排序，對於相同分組字段的結果集進行排序,
其中PARTITION BY 為分組字段，ORDER BY 指定排序字段


over不能單獨使用，要和分析函數：rank(),dense_rank(),row_number()等一起使用。
其參數：over（partition by columnname1 order by columnname2）
含義：按columname1指定的字段進行分組排序，或者說按字段columnname1的值進行分組排序。
例如：employees表中，有兩個部門的記錄：department_id ＝10和20
select department_id，rank（） over（partition by department_id order by salary) from employees就是指在部門10中進行薪水的排名，在部門20中進行薪水排名。如果是partition by org_id，則是在整個公司內進行排名。

SELECT *, Row_Number() OVER (partition by deptid ORDER BY salary desc) rank FROM employee

select ROW_NUMBER() over(order by id1) odid,* from #t1
select ROW_NUMBER() over(partition by id1 order by id1) odid,* from #t1
select ROW_NUMBER() over(partition by id1,id2 order by id1) odid,* from #t1
select ROW_NUMBER() over(partition by id1,id2,id3 order by id1) odid,* from #t1

--ROW_NUMBER 還可以用查重復數據，1代表的是出現的次數,保留id2最大的,並把其他的刪除掉.

delete a from 
(select ROW_NUMBER()over(partition by id1 order by id2 desc) orderid from #t1 ) a
where a.orderid>1

SELECT * FROM (SELECT ROW_NUMBER() OVER(ORDER BY id asc) AS rownum,
id
FROM company ) AS D
WHERE rownum BETWEEN (@pageIndex-1)*@pageSize+1 AND @pageIndex*@pageSize
ORDER BY id asc

with cte as(
    select dense_rank() over(order by Score desc) rank,* from @t
)
select * from cte where rank < 6 　　

SQL over的作用及用法