如何编写包含GROUPBY子句中未包含的列的标准SQL GROUPBY

假设我有一个名为Customer的表，定义如下：

Id       Name       DepartmentId    Hired
1        X          101             2001/01/01
2        Y          102             2002/01/01
3        Z          102             2003/01/01

我想检索每个部门最后一次招聘的日期

显然我会这么做

SELECT c.DepartmentId, MAX(c.Hired)
  FROM Customer c
 GROUP BY c.DepartmentId

返回：

101      2001/01/01
102      2003/01/01

但是如果我想返回被雇佣者的姓名，我该怎么办？即，我希望此结果集：

101      2001/01/01       X
102      2003/01/01       Z

请注意，以下内容不起作用，因为它将返回三行，而不是我要查找的两行：

SELECT c.DepartmentId, c.Name, MAX(c.Hired)
  FROM Customer c
 GROUP BY c.DepartmentId

我不记得看到过实现这一点的查询

---

注意：不接受加入“已雇用”字段，因为这不能保证准确。

一个子选择将完成该工作，并将处理同一部门在同一天雇用多人的情况：

SELECT c.DepartmentId, c.Name, c.Hired from Customer c,
(SELECT DepartmentId, MAX(Hired) as MaxHired
  FROM Customer
 GROUP BY DepartmentId) as sub
WHERE c.DepartmentId = sub.DepartmentId AND c.Hired = sub.MaxHired

标准Sql：

select * 
from Customer C

where exists
(
  -- Linq to Sql put NULL instead ;-) 
  -- In fact, you can even put 1/0 here and would not cause division by zero error
  -- An RDBMS do not parse the select clause of correlated subquery
  SELECT NULL 

  FROM Customer 

  where c.DepartmentId = DepartmentId

  GROUP BY DepartmentId

  having c.Hired = MAX(Hired)
) 

如果Sql Server恰好支持元组测试，这是最简洁的：

select * 
from Customer 
where  (DepartmentId, Hired) in 

(select DepartmentId, MAX(Hired)
 from Customer 
 group by DepartmentId)

---

不相关的问题：可能也不适合加入名称字段。名称不唯一。嵌套选择是您的朋友。此查询返回正确的行数，但可能不会返回正确的值。一些数据库（特别是MySQL）将在ORDERBY子句之前应用GROUPBY。恐怕这不是标准。如果是的话，我就不会问这个问题了。

select * 
from Customer 
where  (DepartmentId, Hired) in 

(select DepartmentId, MAX(Hired)
 from Customer 
 group by DepartmentId)

SELECT a.*
FROM Customer AS a
JOIN
(SELECT DepartmentId, MAX(Hired) AS Hired
FROM Customer GROUP BY DepartmentId) AS b
USING (DepartmentId,Hired);