MySQL中的视图特性和用户权限管理详解

-- 创建部门表
CREATE TABLE DEPT (
    deptno INT PRIMARY KEY,
    dname VARCHAR(20),
    loc VARCHAR(20)
);
-- 创建员工表
CREATE TABLE EMP (
    empno INT PRIMARY KEY,
    ename VARCHAR(20),
    job VARCHAR(20),
    mgr INT,
    hiredate DATE,
    sal DECIMAL(7,2),
    comm DECIMAL(7,2),
    deptno INT,
    FOREIGN KEY (deptno) REFERENCES DEPT(deptno)
);
-- 插入测试数据
INSERT INTO DEPT VALUES
(10, 'ACCOUNTING', 'NEW YORK'),
(20, 'RESEARCH', 'DALLAS'),
(30, 'SALES', 'CHICAGO'),
(40, 'OPERATIONS', 'BOSTON');
INSERT INTO EMP VALUES
(7369, 'SMITH', 'CLERK', 7902, '1980-12-17', 800, NULL, 20),
(7499, 'ALLEN', 'SALESMAN', 7698, '1981-02-20', 1600, 300, 30),
(7521, 'WARD', 'SALESMAN', 7698, '1981-02-22', 1250, 500, 30),
(7566, 'JONES', 'MANAGER', 7839, '1981-04-02', 2975, NULL, 20),
(7654, 'MARTIN', 'SALESMAN', 7698, '1981-09-28', 1250, 1400, 30),
(7698, 'BLAKE', 'MANAGER', 7839, '1981-05-01', 2850, NULL, 30),
(7782, 'CLARK', 'MANAGER', 7839, '1981-06-09', 2450, NULL, 10),
(7788, 'SCOTT', 'ANALYST', 7566, '1987-04-19', 3000, NULL, 20),
(7839, 'KING', 'PRESIDENT', NULL, '1981-11-17', 5000, NULL, 10),
(7844, 'TURNER', 'SALESMAN', 7698, '1981-09-08', 1500, 0, 30),
(7876, 'ADAMS', 'CLERK', 7788, '1987-05-23', 1100, NULL, 20),
(7900, 'JAMES', 'CLERK', 7698, '1981-12-03', 950, NULL, 30),
(7902, 'FORD', 'ANALYST', 7566, '1981-12-03', 3000, NULL, 20),
(7934, 'MILLER', 'CLERK', 7782, '1982-01-23', 1300, NULL, 10);

-- 创建视图
CREATE VIEW v_ename_dname AS
SELECT e.ename, d.dname
FROM EMP e
JOIN DEPT d ON e.deptno = d.deptno;
-- 查询视图（和查询普通表语法完全一致）
SELECT * FROM v_ename_dname ORDER BY dname;

-- 先查看基表中CLARK的信息
SELECT ename FROM EMP WHERE ename = 'CLARK'; -- 结果：CLARK
-- 修改视图中的数据
UPDATE v_ename_dname SET ename = 'TEST' WHERE ename = 'CLARK';
-- 再次查看基表
SELECT ename FROM EMP WHERE ename = 'CLARK'; -- 无结果
SELECT ename FROM EMP WHERE ename = 'TEST';  -- 结果：TEST

-- 修改基表中JAMES的部门编号
UPDATE EMP SET deptno = 10 WHERE ename = 'JAMES';
-- 查询视图中JAMES的部门
SELECT * FROM v_ename_dname WHERE ename = 'JAMES';

-- 删除视图
DROP VIEW v_ename_dname;
-- 验证删除
SHOW TABLES; -- 视图不再出现在列表中

USE mysql;
SELECT host, user, authentication_string FROM user;

-- 创建只能从本机登录的用户dev，密码为Dev@123456
CREATE USER 'dev'@'localhost' IDENTIFIED BY 'Dev@123456';
-- 验证用户创建成功
SELECT host, user FROM mysql.user WHERE user = 'dev';

-- 错误写法（默认匹配%主机，会报错）
DROP USER dev; -- ERROR 1396 (HY000): Operation DROP USER failed for 'dev'@'%'
-- 正确写法（必须完整指定'用户名'@'主机'）
DROP USER 'dev'@'localhost';

-- 1. 用户自己修改自己的密码
SET PASSWORD = PASSWORD('NewDev@123456');
-- 2. root用户修改指定用户的密码
SET PASSWORD FOR 'dev'@'localhost' = PASSWORD('RootSet@123456');

-- 1. 授予dev用户test库所有表的查询权限
GRANT SELECT ON test.* TO 'dev'@'localhost';
-- 2. 授予dev用户test库所有表的增删改查权限
GRANT SELECT, INSERT, UPDATE, DELETE ON test.* TO 'dev'@'localhost';
-- 3. 授予所有库所有权限（生产环境绝对禁止！）
-- GRANT ALL PRIVILEGES ON *.* TO 'dev'@'localhost';
-- 查看用户权限
SHOW GRANTS FOR 'dev'@'localhost';
-- 权限生效（如果授权后不生效，执行此命令）
FLUSH PRIVILEGES;

-- 查看数据库（应该能看到test库）
SHOW DATABASES;
-- 查询test库的表
USE test;
SHOW TABLES;
-- 执行查询（成功）
SELECT * FROM account;
-- 执行删除（如果只给了SELECT权限，会报错）
DELETE FROM account; -- ERROR 1142 (42000): DELETE command denied to user 'dev'@'localhost' for table 'account'

-- 回收dev用户对test库的所有权限
REVOKE ALL ON test.* FROM 'dev'@'localhost';
-- 验证：dev用户执行show databases，只能看到information_schema库
-- 查看权限
SHOW GRANTS FOR 'dev'@'localhost'; -- 显示 GRANT USAGE ON *.* TO 'dev'@'localhost'（USAGE表示无任何权限）