Question

我在涉及3个表的查询时遇到了困难。我需要按部门名称分组每个部门的3个最新用户。这些组应按users.dateadded排序，以便具有最新活动的部门是第一个。用户可以存在于多个部门中，因此我使用的查找表只包含userID和deptID。我的表格如下。

部门 - depID |名称

用户 - userID | name | dateadded

DepUsers - depID | userID

我需要的输出是

接收
John Doe - 4/23/2010
比尔史密斯 - 4/22/2010

会计
史蒂夫琼斯 - 4/22/2010
John Doe - 4/21/2010

审计
史蒂夫琼斯 - 4/21/2010
比尔史密斯 - 4/21/2010

Answer 1

这应该为您提供每个部门最后添加的3个用户（在SQL 2005中使用新的ROW_NUMBER函数）：

select * from (select  D.name, U.name, U.dateadded, ROW_NUMBER() over (PARTITION BY D.depID ORDER BY U.dateadded DESC) as ROWID from Department as D
join DepUsers as DU on DU.depID = D.depID
join Users as U on U.userID = DU.userID) as T
where T.ROWID <= 3

我并不完全明白你希望输出看起来如何，但我想这个结果集可以帮助你开始实现目标。

Answer 2

试试这个：

WITH CTE AS
(
SELECT 
  ROW_NUMBER() OVER (PARTITION BY DepartmentName ORDER BY DateAdded DESC) AS RowNumber
  ,D.name AS DepartmentName
  ,U.name AS UserName
  ,U.dateadded AS DateAdded
FROM 
  DepUsers DU
INNER JOIN Users U
  ON DU.userID = U.userID
INNER JOIN Department D
  ON DU.depID = D.depID
)
SELECT
  DepartmentName
  ,UserName
  ,DateAdded
FROM CTE
WHERE RowNumber <= 3
ORDER BY DepartmentName, DateAdded DESC

SQL 2005：选择前N个，按ID加入组

2 个答案: