Sql 对计数聚合函数使用最小聚合函数

我使用了这个查询：

 select D.DeptID, D.Dept, count(E.EmployeeID) as TotalStaff
 from Employees as E
 right join Departments as D
 on D.DeptID = E.DeptID 
 group by D.DeptID, D.Dept;

要返回此文件：

DeptID_|_Dept___________|TotalStaff
40     | Marketing      | 2
50     | Accounting     | 3
60     | Manager        | 3
70     | GeneralStaff   | 1
80     | HumanResources | 1
90     | Production     | 0
100    | Sales          | 0

现在我想列出部门ID、部门以及员工人数最少的部门的员工人数，因此我尝试了以下方法：

SELECT MIN(mycount) 
FROM 
(
 select D.DeptID, count(E.EmployeeID) as mycount
 from Employees as E
 right join Departments as D
 on D.DeptID = E.DeptID 
 group by D.DeptID
);

但是我得到一个错误，它指出：“；”附近的语法不正确。

---

我所要做的就是返回员工数量最少的部门。请任何人帮我解决这个问题。

您错过了

子查询

别名

所以，您的子查询有这样的别名

SELECT MIN(mycount) 
FROM (select D.DeptID, count(E.EmployeeID) as mycount
      from Employees as E
      right join Departments as D on D.DeptID = E.DeptID 
      group by D.DeptID
     ) s; -- alias missed 

---

编写此查询的正常方法是使用ANSI标准

rank（）

函数：

select d.*
from (select D.DeptID, D.Dept, count(E.EmployeeID) as TotalStaff,
             rank() over (order by count(E.EmployeeID) asc) as seqnum
      from Departments d left join
           Employees E
           on D.DeptID = E.DeptID 
      group by D.DeptID, D.Dept
     ) d
where seqnum = 1;

注意，我还将

连接

切换为

左连接

<代码>左连接通常更容易遵循（至少对于从左到右阅读语言的人来说是这样），因为它表示将所有行保留在第一个表中，而不是最后一个表中。

尝试添加

as tablename

---

在你最后一次考试之后）和期末考试之前

请尝试以下查询：

对于最小值：

 select min(A.mycount) as min_count
    from  (
         select D.DeptID, count(E.EmployeeID) as mycount
         from Departments as D
         left outer join Employees as E on D.DeptID = E.DeptID 
         group by D.DeptID
    ) as A

select max(A.mycount) as max_count
from  (
     select D.DeptID, count(E.EmployeeID) as mycount
     from Departments as D
     left outer join Employees as E on D.DeptID = E.DeptID 
     group by D.DeptID
) as A

对于最大值：

 select min(A.mycount) as min_count
    from  (
         select D.DeptID, count(E.EmployeeID) as mycount
         from Departments as D
         left outer join Employees as E on D.DeptID = E.DeptID 
         group by D.DeptID
    ) as A

select max(A.mycount) as max_count
from  (
     select D.DeptID, count(E.EmployeeID) as mycount
     from Departments as D
     left outer join Employees as E on D.DeptID = E.DeptID 
     group by D.DeptID
) as A

---

为子查询使用名称。您使用的是什么数据库？我使用的是为任务创建的数据库。它已被设置为活动数据库@gordonlinoff，您正在使用哪个？“SQL”只是一种查询语言，而不是特定数据库产品的名称。请为您正在使用的数据库产品添加标记，

postgresql

，

oracle

，

sqlserver

，

db2

。。。