如何根据SQL中的另一列类型计算行数

有没有办法根据SQL中的另一列类型计算行数

数据库：

Department | Resource Type | People
===================================
HR         | manager       | john
           | staff         | jason
           | staff         | smith
IT         | manager       | wendy
           | staff         | emma
           | staff         | jay
           | staff         | cody
HR2        | manager       | john
           | staff         | terry
           | staff         | mike
           | staff         | fry

预期产出：

john, 5 employees
wendy, 3 employees

---

谢谢

根据您的数据样本，请尝试：

SELECT S.Department,
       (SELECT TOP 1 SUB.People FROM dbo.Staff SUB
        WHERE SUB.Department = S.Department 
        AND SUB.ResourceType = 'manager') as Manager,
       COUNT(*) as Employees FROM dbo.Staff S
   WHERE S.ResourceType = 'staff'
   GROUP BY S.Department

我在这里假设，

部门

将包含每个记录的值，而不仅仅是经理的值，每个部门至少有一个经理

---

您可以通过创建两个临时表来完成此操作：

select People, sum(quantity) from(
select [ResourceType], People,quantity
from tablename
right join
(
select Count(Department) quantity, Department
from tablename
group by [ResourceType], Department
having [ResourceType] = 'staff') tmp1 on tablename.Department = tmp1.Department
where [ResourceType] = 'Manager'
) tmp2 
group by People

---

实际上，使用一个连接很容易完成。这还涉及到为两个不同部门的经理工作的员工，以及有多个经理的部门

SELECT t1.People as ManagerName, 
    count(distinct t2.People) 
FROM @Staff t1 
LEFT JOIN @Staff t2 ON t2.Department = t1.department 
    AND t2.ResourceType = 'staff' WHERE t1.ResourceType = 'manager'
GROUP BY t1.People

---

与其他答案一样，我还必须假设所有行在

Department

列中都有一个值。否则，就没有办法按你的要求去做

此外，您的示例数据似乎暗示每个部门只有一名经理。所以我也会做出这样的假设

执行此操作的简单查询如下：

select mgr.people || ', ' ||
       count(staff.people) || ' employees' -- the string concatenation on these lines may vary depending on your database.
  from TableName mgr
  left join TableName staff
    on staff.Department = mgr.Department
   and staff.ResourceType = 'staff'
 where mgr.ResourceType = 'manager'
 group by mgr.people

---

在您的数据中，哪些列值建立了经理和员工之间的关系？我没有看到。员工的

department

列真的是

null

吗？department列中缺少值。您使用的是哪种DBMS？博士后？神谕