窗口函数小结

样本数据库下载：

http://files.cnblogs.com/files/haseo/TSQL2012.rar

1.窗口聚合函数

除了多个OVER子句其实和分组聚合函数一样。

SELECT  custid ,
        orderid ,
        val ,
        SUM(val) OVER ( PARTITION BY custid ) AS custtotal ,
        SUM(val) OVER ( ) AS grandtotal
FROM    Sales.OrderValues;

SELECT  custid ,
        orderid ,
        val ,
        CAST(100.0 * val / SUM(val) OVER ( PARTITION BY custid ) AS NUMERIC(5,2)) AS pctcust ,
        CAST(100.0 * val / SUM(val) OVER ( ) AS NUMERIC(5, 2)) AS pcttotal
FROM    Sales.OrderValues;

框架限定（必须要排序）

UNBOUNDED PRECEDING   统计之前所有记录

<n> ROWS PRECEDING 统计前面几行

CURRENT ROW  当前行

UNBOUNDED FOLLOWING 本组下一行

SELECT  custid ,
        orderid ,
        orderdate ,
        val ,
        SUM(val) OVER ( PARTITION BY custid ORDER BY orderdate, orderid
ROWS BETWEEN UNBOUNDED PRECEDING AND CURRENT ROW  --可以直接简写为 ROWS UNBOUNDED PRECEDING
--ROWS  BETWEEN 2 PRECEDING AND CURRENT ROW
) AS runningtotal
FROM    Sales.OrderValues;

2.排名函数

SELECT  custid ,
        orderid ,
        val ,
        ROW_NUMBER() OVER ( ORDER BY val ) AS rownum ,
        RANK() OVER ( ORDER BY val ) AS rnk ,
        DENSE_RANK() OVER ( ORDER BY val ) AS densernk ,
        NTILE(100) OVER ( ORDER BY val ) AS ntile100 --分割结果，列子中分了一百组
FROM    Sales.OrderValues;

3.偏移函数

SELECT  custid ,
        orderid ,
        orderdate ,
        val ,
        LAG(val) OVER ( PARTITION BY custid ORDER BY orderdate, orderid ) AS prev_val ,--显示前一行
        --显示前三行LAG(val, 3)，如过值不存在设置默认值为0  LAG(val, 3, 0).
        LEAD(val) OVER ( PARTITION BY custid ORDER BY orderdate, orderid ) AS next_val --显示后一行
FROM    Sales.OrderValues;

--FIRST_VALUE 和 LAST_VALUE支持window partition,order, and frame clauses.
SELECT  custid ,
        orderid ,
        orderdate ,
        val ,
        FIRST_VALUE(val) OVER ( PARTITION BY custid ORDER BY orderdate, orderid
ROWS BETWEEN UNBOUNDED PRECEDING
AND CURRENT ROW ) AS first_val ,
        LAST_VALUE(val) OVER ( PARTITION BY custid ORDER BY orderdate, orderid
ROWS BETWEEN CURRENT ROW
AND UNBOUNDED FOLLOWING ) AS last_val
FROM    Sales.OrderValues;