如何在关系表中显示数据

-- 创建 Employees 表
CREATE TABLE Employees (
    EmployeeID INT PRIMARY KEY,
    FirstName VARCHAR(50),
    LastName VARCHAR(50),
    DepartmentID INT
);

-- 创建 Departments 表
CREATE TABLE Departments (
    DepartmentID INT PRIMARY KEY,
    DepartmentName VARCHAR(50)
);

-- 插入示例数据
INSERT INTO Employees (EmployeeID, FirstName, LastName, DepartmentID) VALUES
(1, 'John', 'Doe', 1),
(2, 'Jane', 'Smith', 2);

INSERT INTO Departments (DepartmentID, DepartmentName) VALUES
(1, 'HR'),
(2, 'Engineering');

-- 查询并显示每个员工及其所属部门的信息
SELECT e.FirstName, e.LastName, d.DepartmentName
FROM Employees e
JOIN Departments d ON e.DepartmentID = d.DepartmentID;

SELECT DISTINCT e.FirstName, e.LastName, d.DepartmentName
FROM Employees e
JOIN Departments d ON e.DepartmentID = d.DepartmentID;

CREATE INDEX idx_DepartmentID ON Employees(DepartmentID);