SQL over的作用及用法

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 )
可实现按指定的字段分组排序，对于相同分组字段的结果集进行排序,
其中PARTITION BY 为分组字段，ORDER BY 指定排序字段


over不能单独使用，要和分析函数：rank(),dense_rank(),row_number()等一起使用。
其参数：over（partition by columnname1 order by columnname2）
含义：按columname1指定的字段进行分组排序，或者说按字段columnname1的值进行分组排序。
例如：employees表中，有两个部门的记录：department_id ＝10和20
select department_id，rank（） over（partition by department_id order by salary) from employees就是指在部门10中进行薪水的排名，在部门20中进行薪水排名。如果是partition by org_id，则是在整个公司内进行排名。

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 还可以用查重复数据，1代表的是出现的次数,保留id2最大的,并把其他的删除掉.

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