如何返回每个部门名称和每个部门的员工人数

Question

给定以下结构，尝试制作一个显示每个部门名称和每个部门员工人数的程序。

尝试了下面的代码，但没有按预期工作。

CREATE PROCEDURE SelectDepartmentNameandEmployee
AS
SELECT name
FROM Department
JOIN Employees as e
        on d.departmentID = e.departmentID

表结构

[Department]
(
    [departmentID] INT IDENTITY (1, 1) NOT NULL PRIMARY KEY,
    [name] VARCHAR(50) NOT NULL,
    [costCentreID] INT FOREIGN KEY REFERENCES CostCentre(costCentreID)
);



[Employees]
(
    [employeeNo] INT IDENTITY (1, 1) NOT NULL PRIMARY KEY,
    [lastName] VARCHAR(50) NOT NULL,
    [firstName] VARCHAR(50) NOT NULL,
    [gender] CHAR NOT NULL,
    [IDNumber] VARCHAR(20) NOT NULL,
    [salaryLevelID] INT,
    [departmentID] INT FOREIGN KEY REFERENCES Department(departmentID)
);

Answer 1

这是一个简单的聚合查询。你的失败是因为：

• 缺少GROUP BY 子句
• 查询中未定义表别名d

考虑：

SELECT d.name, COUNT(*) no_employees
FROM Department d
INNER JOIN Employees as e ON d.departmentID = e.departmentID
GROUP BY d.departmentID, d.name

如果您还想显示没有员工的部门，那么：

SELECT d.name, COUNT(e.departmentID) no_employees
FROM Department d
LEFT JOIN Employees as e ON d.departmentID = e.departmentID
GROUP BY d.departmentID, d.name