Window offset 函数包括两类，一类是计算相对于当前行的偏移位置，一类则是相对于window frame的起点或是终点。

第一类包括 LAG和LEAD这两个函数，第二类包括FIRST_VALUE, LAST_VALUE和 NTH_VALUE,在SQL server 2012中没有实现NTH_VALUE。

Example for LAG and LEAD:

SELECT custid, orderdate, orderid, val,

LAG(val) OVER(PARTITION BY custid ORDER BY orderdate, orderid) AS prevval,

                    LEAD(val) OVER(PARTITION BY custid
           ORDER BY orderdate, orderid) AS nextval
           FROM Sales.OrderValues;

Result:

example for FIRST_VALUE, LAST_VALUE:

SELECT custid, orderdate, orderid, val,
FIRST_VALUE(val) OVER(PARTITION BY custid
ORDER BY orderdate, orderid) AS val_firstorder,
LAST_VALUE(val) OVER(PARTITION BY custid
ORDER BY orderdate, orderid
ROWS BETWEEN CURRENT ROW
AND UNBOUNDED FOLLOWING) AS val_lastorder
FROM Sales.OrderValues
order by custid,val

Result：

这个结果很好体会，因此不赘述

CONT.jpg

FIRST_VALUE.jpg

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介绍SQl server 2012的新分析函数--Offset Functions

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