LAST_VALUE (Transact-SQL)
返回 SQL Server 2012 中有序值集中的最后一个值。
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语法
LAST_VALUE ( [scalar_expression )
OVER ( [ partition_by_clause ] order_by_clause rows_range_clause )
参数
scalar_expression
是要返回的值。scalar_expression 可以是产生单个值的列、子查询或其他表达式。不允许使用其他分析函数。OVER ( [ partition_by_clause ] order_by_clause [ rows_range_clause ] )
partition_by_clause 将由 FROM 子句生成的结果集划分成 RANK 函数适用的分区。如果未指定，则此函数将查询结果集的所有行视为单个组。order_by_clause 在应用函数之前确定数据的顺序。order_by_clause 是必需的。rows_range_clause 通过指定起点和终点，限制分区中的行数。有关详细信息，请参阅OVER 子句 (Transact-SQL)。
返回类型
与 scalar_expression 类型相同。
示例
A. 对分区使用 LAST_VALUE
下面的示例给定每个部门中给定薪金（比率）的最后一个雇员的雇佣日期。PARTITION BY 子句按部门对员工分区，而 LAST_VALUE 函数独立应用于每个分区。在 OVER 子句中指定的 ORDER BY 子句确定对每个分区中的行应用 LAST_VALUE 函数的逻辑顺序。
USE AdventureWorks2012;
GO
SELECT Department, LastName, Rate, HireDate,
LAST_VALUE(HireDate) OVER (PARTITION BY Department ORDER BY Rate) AS LastValue
FROM HumanResources.vEmployeeDepartmentHistory AS edh
INNER JOIN HumanResources.EmployeePayHistory AS eph
ON eph.BusinessEntityID = edh.BusinessEntityID
INNER JOIN HumanResources.Employee AS e
ON e.BusinessEntityID = edh.BusinessEntityID
WHERE Department IN (N'Information Services',N'Document Control');
下面是结果集。
Department LastName Rate HireDate LastValue
--------------------------- ----------------------- ------------ ---------- ----------
Document Control Chai 10.25 2003-02-23 2003-03-13
Document Control Berge 10.25 2003-03-13 2003-03-13
Document Control Norred 16.8269 2003-04-07 2003-01-17
Document Control Kharatishvili 16.8269 2003-01-17 2003-01-17
Document Control Arifin 17.7885 2003-02-05 2003-02-05
Information Services Berg 27.4038 2003-03-20 2003-01-24
Information Services Meyyappan 27.4038 2003-03-07 2003-01-24
Information Services Bacon 27.4038 2003-02-12 2003-01-24
Information Services Bueno 27.4038 2003-01-24 2003-01-24
Information Services Sharma 32.4519 2003-01-05 2003-03-27
Information Services Connelly 32.4519 2003-03-27 2003-03-27
Information Services Ajenstat 38.4615 2003-02-18 2003-02-23
Information Services Wilson 38.4615 2003-02-23 2003-02-23
Information Services Conroy 39.6635 2003-03-08 2003-03-08
Information Services Trenary 50.4808 2003-01-12 2003-01-12
B. 在计算表达式中使用 FIRST_VALUE 和 LAST_VALUE
以下示例在计算表达式中使用 FIRST_VALUE 和 LAST_VALUE 函数，显示给定数量的员工当前季度分别与一年中第一季度和最后一季度之间的销售配额值差异。FIRST_VALUE 函数返回该年度第一季度的销售配额值，并将该值从当前季度的销售配额值中减去。它在名为 DifferenceFromFirstQuarter 的派生列中返回。对于一年的第一季度，DifferenceFromFirstQuarter 列的值为 0。LAST_VALUE 函数返回该年度最后一个季度的销售配额值，并从当前季度的销售配额值中减去它。它在名为 DifferenceFromLastQuarter 的派生列中返回。对于一年的最后一个季度，DifferenceFromLastQuarter 列的值为 0。
如下所示，对于要在 DifferenceFromLastQuarter 列中返回的非零值，子句“RANGE BETWEEN CURRENT ROW AND UNBOUNDED FOLLOWING”在此示例中是必需的。默认范围为“RANGE BETWEEN UNBOUNDED PRECEDING AND CURRENT ROW”。在此示例中，使用默认范围（或不包括范围，导致使用默认范围）将导致在 DifferenceFromLastQuarter 列中返回零。有关详细信息，请参阅OVER 子句 (Transact-SQL)。
USE AdventureWorks2012;
SELECT BusinessEntityID, DATEPART(QUARTER,QuotaDate)AS Quarter, YEAR(QuotaDate) AS SalesYear,
SalesQuota AS QuotaThisQuarter,
SalesQuota - FIRST_VALUE(SalesQuota)
OVER (PARTITION BY BusinessEntityID, YEAR(QuotaDate)
ORDER BY DATEPART(QUARTER,QuotaDate) ) AS DifferenceFromFirstQuarter,
SalesQuota - LAST_VALUE(SalesQuota)
OVER (PARTITION BY BusinessEntityID, YEAR(QuotaDate)
ORDER BY DATEPART(QUARTER,QuotaDate)
RANGE BETWEEN CURRENT ROW AND UNBOUNDED FOLLOWING ) AS DifferenceFromLastQuarter
FROM Sales.SalesPersonQuotaHistory
WHERE YEAR(QuotaDate) > 2005
AND BusinessEntityID BETWEEN 274 AND 275
ORDER BY BusinessEntityID, SalesYear, Quarter;
下面是结果集。
BusinessEntityID Quarter SalesYear QuotaThisQuarter DifferenceFromFirstQuarter DifferenceFromLastQuarter
---------------- ----------- ----------- --------------------- --------------------------- -----------------------
274 1 2006 91000.00 0.00 -63000.00
274 2 2006 140000.00 49000.00 -14000.00
274 3 2006 70000.00 -21000.00 -84000.00
274 4 2006 154000.00 63000.00 0.00
274 1 2007 107000.00 0.00 -9000.00
274 2 2007 58000.00 -49000.00 -58000.00
274 3 2007 263000.00 156000.00 147000.00
274 4 2007 116000.00 9000.00 0.00
274 1 2008 84000.00 0.00 -103000.00
274 2 2008 187000.00 103000.00 0.00
275 1 2006 502000.00 0.00 -822000.00
275 2 2006 550000.00 48000.00 -774000.00
275 3 2006 1429000.00 927000.00 105000.00
275 4 2006 1324000.00 822000.00 0.00
275 1 2007 729000.00 0.00 -489000.00
275 2 2007 1194000.00 465000.00 -24000.00
275 3 2007 1575000.00 846000.00 357000.00
275 4 2007 1218000.00 489000.00 0.00
275 1 2008 849000.00 0.00 -20000.00
275 2 2008 869000.00 20000.00 0.00
(20 row(s) affected)