MySQL 学习 - 技术栈

文章目录

- [一、SQL 基础](#一、SQL 基础)
- - [1.1 SQL 语法规范](#1.1 SQL 语法规范)
  - [1.2 SQL 分类体系](#1.2 SQL 分类体系)
- 二、数据库管理（DDL）
- - [2.1 数据库生命周期管理](#2.1 数据库生命周期管理)
  - - [2.1.1 创建数据库](#2.1.1 创建数据库)
    - [2.1.2 数据库维护](#2.1.2 数据库维护)
    - [2.1.3 数据库连接管理](#2.1.3 数据库连接管理)
  - [2.2 表结构设计与管理](#2.2 表结构设计与管理)
  - - [2.2.1 数据类型详解](#2.2.1 数据类型详解)
    - [2.2.2 创建表](#2.2.2 创建表)
    - [2.2.3 表结构维护](#2.2.3 表结构维护)
- 三、数据操作（DML）
- - [3.1 插入数据](#3.1 插入数据)
  - [3.2 更新数据](#3.2 更新数据)
  - [3.3 删除数据](#3.3 删除数据)
- 四、数据查询（DQL）
- - [4.1 查询基础](#4.1 查询基础)
  - - [4.1.1 基本语法结构](#4.1.1 基本语法结构)
    - [4.1.2 选择列](#4.1.2 选择列)
  - [4.2 条件查询](#4.2 条件查询)
  - - [4.2.1 比较运算符](#4.2.1 比较运算符)
    - [4.2.2 范围查询](#4.2.2 范围查询)
    - [4.2.3 模糊查询](#4.2.3 模糊查询)
  - [4.3 排序与分页](#4.3 排序与分页)
  - - [4.3.1 排序](#4.3.1 排序)
    - [4.3.2 分页查询](#4.3.2 分页查询)
  - [4.4 聚合查询](#4.4 聚合查询)
  - - [4.4.1 聚合函数](#4.4.1 聚合函数)
    - [4.4.2 分组查询](#4.4.2 分组查询)
  - [4.5 连接查询](#4.5 连接查询)
  - - [4.5.1 内连接](#4.5.1 内连接)
    - [4.5.2 外连接](#4.5.2 外连接)
    - [4.5.3 交叉连接](#4.5.3 交叉连接)
  - [4.6 子查询](#4.6 子查询)
  - - [4.6.1 标量子查询](#4.6.1 标量子查询)
    - [4.6.2 行子查询](#4.6.2 行子查询)
    - [4.6.3 表子查询](#4.6.3 表子查询)
    - [4.6.4 相关子查询](#4.6.4 相关子查询)
  - [4.7 集合操作](#4.7 集合操作)
- 五、高级特性
- - [5.1 视图](#5.1 视图)
  - [5.2 索引](#5.2 索引)
  - [5.3 事务控制](#5.3 事务控制)
  - [5.4 存储过程与函数](#5.4 存储过程与函数)
- 六、性能优化
- - [6.1 查询优化原则](#6.1 查询优化原则)
  - [6.2 索引优化策略](#6.2 索引优化策略)
  - [6.3 查询缓存](#6.3 查询缓存)
- 七、安全管理
- - [7.1 用户权限管理](#7.1 用户权限管理)
  - [7.2 数据备份与恢复](#7.2 数据备份与恢复)

一、SQL 基础

1.1 SQL 语法规范

sql 复制代码

-- 书写规范
SELECT * FROM users;  -- 以分号结尾
SELECT *              -- 可多行书写
  FROM users
 WHERE age > 18;
 
-- 大小写（建议）
SELECT * FROM users;  -- 关键字大写，表名小写
select * from users;  -- MySQL 不区分，都可执行

1.2 SQL 分类体系

类别	全称	作用	关键命令
DDL	数据定义语言	定义数据库对象	CREATE, DROP, ALTER
DML	数据操纵语言	操作数据记录	INSERT, DELETE, UPDATE
DQL	数据查询语言	查询数据	SELECT, WHERE, JOIN
DCL	数据控制语言	控制访问权限	GRANT, REVOKE

二、数据库管理（DDL）

2.1 数据库生命周期管理

2.1.1 创建数据库

sql 复制代码

-- 基础创建
CREATE DATABASE school;

-- 安全创建（避免重复）
CREATE DATABASE IF NOT EXISTS school;

-- 创建时指定字符集
CREATE DATABASE school 
  CHARACTER SET utf8mb4 
  COLLATE utf8mb4_unicode_ci;

-- 完整语法
CREATE DATABASE [IF NOT EXISTS] database_name
  [CHARACTER SET charset_name]
  [COLLATE collation_name];

2.1.2 数据库维护

sql 复制代码

-- 查询所有数据库
SHOW DATABASES;

-- 查看数据库信息
SHOW CREATE DATABASE school;

-- 修改数据库字符集
ALTER DATABASE school CHARACTER SET utf8;

-- 删除数据库
DROP DATABASE school;
DROP DATABASE IF EXISTS school;  -- 安全删除

2.1.3 数据库连接管理

sql 复制代码

-- 使用数据库
USE school;

-- 查看当前数据库
SELECT DATABASE();

-- 查看连接信息
SHOW PROCESSLIST;

2.2 表结构设计与管理

2.2.1 数据类型详解

类别	类型	描述	示例
数值型	INT	整数	`age INT`
	BIGINT	大整数	`id BIGINT`
	DECIMAL	精确小数	`price DECIMAL(10,2)`
	FLOAT/DOUBLE	浮点数	`score DOUBLE`
字符串	CHAR	定长字符串	`gender CHAR(1)`
	VARCHAR	变长字符串	`name VARCHAR(50)`
	TEXT	长文本	`content TEXT`
日期时间	DATE	日期	`birthday DATE`
	DATETIME	日期时间	`create_time DATETIME`
	TIMESTAMP	时间戳	`update_time TIMESTAMP`
其他	BLOB	二进制数据	`image BLOB`
	BOOLEAN	布尔值	`is_active BOOLEAN`

2.2.2 创建表

sql 复制代码

-- 基础表创建
CREATE TABLE students (
    id INT PRIMARY KEY AUTO_INCREMENT,
    name VARCHAR(50) NOT NULL,
    age INT DEFAULT 18,
    email VARCHAR(100) UNIQUE,
    created_at TIMESTAMP DEFAULT CURRENT_TIMESTAMP,
    updated_at TIMESTAMP DEFAULT CURRENT_TIMESTAMP 
      ON UPDATE CURRENT_TIMESTAMP
);

-- 带索引和约束
CREATE TABLE courses (
    course_id INT PRIMARY KEY,
    course_name VARCHAR(100) NOT NULL,
    credit DECIMAL(3,1),
    teacher_id INT,
    INDEX idx_teacher (teacher_id),
    CONSTRAINT chk_credit CHECK (credit BETWEEN 0 AND 10)
);

2.2.3 表结构维护

sql 复制代码

-- 查看表结构
DESC students;
DESCRIBE students;
SHOW COLUMNS FROM students;

-- 查看建表语句
SHOW CREATE TABLE students;

-- 修改表名
ALTER TABLE students RENAME TO new_students;
RENAME TABLE students TO new_students;

-- 修改表字符集
ALTER TABLE students CHARACTER SET utf8mb4;

-- 添加列
ALTER TABLE students ADD COLUMN phone VARCHAR(20);

-- 修改列
ALTER TABLE students CHANGE COLUMN phone mobile VARCHAR(15);
ALTER TABLE students MODIFY COLUMN mobile VARCHAR(20);

-- 删除列
ALTER TABLE students DROP COLUMN mobile;

-- 复制表结构
CREATE TABLE students_backup LIKE students;

-- 复制表结构和数据
CREATE TABLE students_copy AS SELECT * FROM students;

-- 删除表
DROP TABLE IF EXISTS students;

三、数据操作（DML）

3.1 插入数据

sql 复制代码

-- 指定列插入
INSERT INTO students (name, age, email) 
VALUES ('张三', 20, 'zhangsan@example.com');

-- 插入多行数据
INSERT INTO students (name, age, email) VALUES
('李四', 21, 'lisi@example.com'),
('王五', 22, 'wangwu@example.com'),
('赵六', 23, 'zhaoliu@example.com');

-- 插入查询结果
INSERT INTO student_archive 
SELECT * FROM students WHERE graduation_year < 2020;

-- 使用 SET 语法
INSERT INTO students 
SET name = '张三', age = 20, email = 'zhangsan@example.com';

-- 忽略重复键
INSERT IGNORE INTO students (id, name) VALUES (1, '张三');

3.2 更新数据

sql 复制代码

-- 单表更新
UPDATE students 
SET age = age + 1, 
    updated_at = NOW() 
WHERE id = 1;

-- 使用子查询更新
UPDATE students s
JOIN classes c ON s.class_id = c.id
SET s.status = 'graduated'
WHERE c.graduation_year = 2023;

-- 批量更新
UPDATE products 
SET price = price * 0.9 
WHERE category = 'electronics';

-- 使用 CASE 条件更新
UPDATE students 
SET grade = CASE 
    WHEN score >= 90 THEN 'A'
    WHEN score >= 80 THEN 'B'
    WHEN score >= 70 THEN 'C'
    ELSE 'D'
END;

3.3 删除数据

sql 复制代码

-- 条件删除
DELETE FROM students WHERE id = 1;

-- 关联删除
DELETE s FROM students s
JOIN scores sc ON s.id = sc.student_id
WHERE sc.score < 60;

-- 清空表数据的不同方式
DELETE FROM students;      -- 逐行删除，可回滚
TRUNCATE TABLE students;   -- 快速清空，不可回滚
DROP TABLE students;       -- 删除表结构和数据

-- 使用 JOIN 删除
DELETE s, sc 
FROM students s
LEFT JOIN scores sc ON s.id = sc.student_id
WHERE s.graduation_year < 2020;

四、数据查询（DQL）

4.1 查询基础

4.1.1 基本语法结构

sql 复制代码

SELECT [DISTINCT] column_list
FROM table_references
[WHERE where_condition]
[GROUP BY {col_name | expr | position}]
[HAVING having_condition]
[ORDER BY {col_name | expr | position} [ASC | DESC]]
[LIMIT {[offset,] row_count | row_count OFFSET offset}]
[FOR UPDATE | LOCK IN SHARE MODE]

4.1.2 选择列

sql 复制代码

-- 选择所有列
SELECT * FROM students;

-- 选择特定列
SELECT id, name, age FROM students;

-- 使用表达式
SELECT 
    name,
    age,
    YEAR(NOW()) - YEAR(birthdate) AS current_age,
    CONCAT(name, '(', age, ')') AS name_with_age
FROM students;

-- 去除重复
SELECT DISTINCT class_id FROM students;

-- 使用别名
SELECT 
    s.name AS student_name,
    c.name AS class_name
FROM students s
JOIN classes c ON s.class_id = c.id;

4.2 条件查询

4.2.1 比较运算符

sql 复制代码

-- 基本比较
SELECT * FROM students WHERE age > 20;
SELECT * FROM products WHERE price <= 100;
SELECT * FROM users WHERE status = 'active';

-- NULL 值处理
SELECT * FROM students WHERE email IS NULL;
SELECT * FROM students WHERE email IS NOT NULL;

-- NULL 安全比较
SELECT * FROM students WHERE age <=> NULL;

4.2.2 范围查询

sql 复制代码

-- BETWEEN
SELECT * FROM students WHERE age BETWEEN 18 AND 25;

-- IN
SELECT * FROM students WHERE class_id IN (1, 3, 5);
SELECT * FROM students WHERE class_id NOT IN (2, 4);

-- 使用子查询
SELECT * FROM students 
WHERE class_id IN (SELECT id FROM classes WHERE teacher = '王老师');

4.2.3 模糊查询

sql 复制代码

-- % 匹配任意字符
SELECT * FROM students WHERE name LIKE '张%';
SELECT * FROM students WHERE name LIKE '%三%';

-- _ 匹配单个字符
SELECT * FROM students WHERE name LIKE '_三';
SELECT * FROM students WHERE name LIKE '张_';

-- 转义特殊字符
SELECT * FROM products WHERE name LIKE '%100%%' ESCAPE '';

-- 正则表达式
SELECT * FROM students WHERE name REGEXP '^张';
SELECT * FROM students WHERE email REGEXP '@gmail\.com$';

4.3 排序与分页

4.3.1 排序

sql 复制代码

-- 单字段排序
SELECT * FROM students ORDER BY age DESC;

-- 多字段排序
SELECT * FROM students 
ORDER BY class_id ASC, score DESC;

-- 使用表达式排序
SELECT * FROM students 
ORDER BY 
    CASE WHEN grade = 'A' THEN 1
         WHEN grade = 'B' THEN 2
         ELSE 3
    END,
    score DESC;

-- NULL 值排序
SELECT * FROM students 
ORDER BY score IS NULL, score DESC;

4.3.2 分页查询

sql 复制代码

-- 基础分页
SELECT * FROM students LIMIT 10 OFFSET 0;   -- 第1页
SELECT * FROM students LIMIT 10 OFFSET 10;  -- 第2页

-- 简写形式
SELECT * FROM students LIMIT 0, 10;   -- 第1页
SELECT * FROM students LIMIT 10, 10;  -- 第2页

-- 动态分页
SET @page = 2;
SET @page_size = 10;
SELECT * FROM students 
LIMIT @page_size 
OFFSET (@page - 1) * @page_size;

-- 结合排序的分页
SELECT * FROM students 
ORDER BY created_at DESC 
LIMIT 10 OFFSET 0;

4.4 聚合查询

4.4.1 聚合函数

sql 复制代码

-- COUNT 计数
SELECT COUNT(*) FROM students;
SELECT COUNT(DISTINCT class_id) FROM students;
SELECT COUNT(id) FROM students WHERE age > 20;

-- SUM 求和
SELECT SUM(score) FROM exams;
SELECT SUM(score) AS total_score FROM exams WHERE student_id = 1;

-- AVG 平均值
SELECT AVG(score) FROM exams;
SELECT AVG(score) AS average_score FROM exams WHERE exam_date = '2023-06-01';

-- MAX/MIN 最值
SELECT MAX(score), MIN(score) FROM exams;
SELECT name, MAX(score) AS highest_score FROM students s
JOIN exams e ON s.id = e.student_id
GROUP BY s.id;

-- GROUP_CONCAT 组内连接
SELECT class_id, 
       GROUP_CONCAT(name ORDER BY score DESC) AS student_list
FROM students
GROUP BY class_id;

4.4.2 分组查询

sql 复制代码

-- 基本分组
SELECT class_id, COUNT(*) AS student_count
FROM students
GROUP BY class_id;

-- 多字段分组
SELECT class_id, gender, COUNT(*) AS count
FROM students
GROUP BY class_id, gender;

-- HAVING 筛选分组
SELECT class_id, AVG(score) AS avg_score
FROM students
GROUP BY class_id
HAVING AVG(score) > 80;

-- ROLLUP 汇总
SELECT class_id, gender, COUNT(*) 
FROM students
GROUP BY class_id, gender WITH ROLLUP;

-- 分组排序
SELECT class_id, name, score
FROM students
ORDER BY class_id, score DESC;

4.5 连接查询

4.5.1 内连接

sql 复制代码

-- 等值连接
SELECT s.name, c.class_name
FROM students s
INNER JOIN classes c ON s.class_id = c.id;

-- 多表连接
SELECT s.name, c.class_name, t.teacher_name
FROM students s
INNER JOIN classes c ON s.class_id = c.id
INNER JOIN teachers t ON c.teacher_id = t.id;

-- 自连接
SELECT e1.employee_name, e2.employee_name AS manager_name
FROM employees e1
INNER JOIN employees e2 ON e1.manager_id = e2.id;

4.5.2 外连接

sql 复制代码

-- 左外连接
SELECT s.name, c.class_name
FROM students s
LEFT JOIN classes c ON s.class_id = c.id;

-- 右外连接
SELECT s.name, c.class_name
FROM students s
RIGHT JOIN classes c ON s.class_id = c.id;

-- 全外连接（MySQL 模拟）
SELECT s.name, c.class_name
FROM students s
LEFT JOIN classes c ON s.class_id = c.id
UNION
SELECT s.name, c.class_name
FROM students s
RIGHT JOIN classes c ON s.class_id = c.id
WHERE s.id IS NULL;

4.5.3 交叉连接

sql 复制代码

-- 显式交叉连接
SELECT s.name, c.course_name
FROM students s
CROSS JOIN courses c;

-- 隐式交叉连接
SELECT s.name, c.course_name
FROM students s, courses c;

4.6 子查询

4.6.1 标量子查询

sql 复制代码

-- WHERE 子句
SELECT * FROM students 
WHERE age > (SELECT AVG(age) FROM students);

-- SELECT 子句
SELECT name,
       (SELECT COUNT(*) FROM scores WHERE student_id = s.id) AS score_count
FROM students s;

-- HAVING 子句
SELECT class_id, AVG(score)
FROM students
GROUP BY class_id
HAVING AVG(score) > (SELECT AVG(score) FROM students);

4.6.2 行子查询

sql 复制代码

SELECT * FROM students 
WHERE (class_id, score) IN (
    SELECT class_id, MAX(score)
    FROM students
    GROUP BY class_id
);

4.6.3 表子查询

sql 复制代码

-- 派生表
SELECT s.name, t.avg_score
FROM students s
JOIN (
    SELECT student_id, AVG(score) AS avg_score
    FROM scores
    GROUP BY student_id
    HAVING AVG(score) > 80
) t ON s.id = t.student_id;

-- 使用 WITH 子句（CTE）
WITH top_students AS (
    SELECT student_id, AVG(score) AS avg_score
    FROM scores
    GROUP BY student_id
    HAVING AVG(score) > 90
)
SELECT s.name, ts.avg_score
FROM students s
JOIN top_students ts ON s.id = ts.student_id;

4.6.4 相关子查询

sql 复制代码

-- EXISTS
SELECT * FROM students s
WHERE EXISTS (
    SELECT 1 FROM scores sc
    WHERE sc.student_id = s.id AND sc.score = 100
);

-- NOT EXISTS
SELECT * FROM classes c
WHERE NOT EXISTS (
    SELECT 1 FROM students s
    WHERE s.class_id = c.id AND s.gender = '女'
);

4.7 集合操作

sql 复制代码

-- UNION（去重）
SELECT name FROM current_students
UNION
SELECT name FROM graduated_students;

-- UNION ALL（不去重）
SELECT name FROM current_students
UNION ALL
SELECT name FROM graduated_students;

-- INTERSECT（交集）- MySQL 8.0+
SELECT name FROM students
INTERSECT
SELECT name FROM honors_students;

-- EXCEPT（差集）- MySQL 8.0+
SELECT name FROM students
EXCEPT
SELECT name FROM failed_students;

五、高级特性

5.1 视图

sql 复制代码

-- 创建视图
CREATE VIEW student_scores AS
SELECT s.name, sc.course, sc.score
FROM students s
JOIN scores sc ON s.id = sc.student_id;

-- 带检查选项
CREATE VIEW active_students AS
SELECT * FROM students WHERE status = 'active'
WITH CHECK OPTION;

-- 更新视图
ALTER VIEW student_scores AS
SELECT s.name, sc.course, sc.score, sc.exam_date
FROM students s
JOIN scores sc ON s.id = sc.student_id;

-- 删除视图
DROP VIEW IF EXISTS student_scores;

5.2 索引

sql 复制代码

-- 创建索引
CREATE INDEX idx_student_name ON students(name);
CREATE INDEX idx_student_class ON students(class_id, name);
CREATE FULLTEXT INDEX idx_content ON articles(content);

-- 查看索引
SHOW INDEX FROM students;

-- 删除索引
DROP INDEX idx_student_name ON students;

-- 分析索引使用
EXPLAIN SELECT * FROM students WHERE name = '张三';

5.3 事务控制

sql 复制代码

-- 开启事务
START TRANSACTION;
BEGIN;

-- 设置保存点
SAVEPOINT sp1;

-- 回滚到保存点
ROLLBACK TO sp1;

-- 提交事务
COMMIT;

-- 设置事务隔离级别
SET TRANSACTION ISOLATION LEVEL READ COMMITTED;
SET SESSION TRANSACTION ISOLATION LEVEL REPEATABLE READ;

-- 查看隔离级别
SELECT @@transaction_isolation;

5.4 存储过程与函数

sql 复制代码

-- 创建存储过程
DELIMITER //
CREATE PROCEDURE GetStudentCount(IN classId INT, OUT total INT)
BEGIN
    SELECT COUNT(*) INTO total 
    FROM students 
    WHERE class_id = classId;
END //
DELIMITER ;

-- 调用存储过程
CALL GetStudentCount(1, @count);
SELECT @count;

-- 创建函数
DELIMITER //
CREATE FUNCTION GetStudentName(studentId INT)
RETURNS VARCHAR(50)
READS SQL DATA
BEGIN
    DECLARE studentName VARCHAR(50);
    SELECT name INTO studentName 
    FROM students 
    WHERE id = studentId;
    RETURN studentName;
END //
DELIMITER ;

-- 使用函数
SELECT GetStudentName(1);

六、性能优化

6.1 查询优化原则

使用合适的索引
避免 SELECT
合理使用 JOIN
避免在 WHERE 子句中使用函数
使用 EXPLAIN 分析查询

6.2 索引优化策略

sql 复制代码

-- 复合索引最左前缀原则
CREATE INDEX idx_name_age ON students(name, age);
-- 有效查询: WHERE name = ? AND age = ?
-- 有效查询: WHERE name = ?
-- 无效查询: WHERE age = ?

-- 覆盖索引
CREATE INDEX idx_covering ON students(name, age, email);
SELECT name, age FROM students WHERE name = '张三'; -- 使用覆盖索引

-- 索引下推（MySQL 5.6+）
SET optimizer_switch = 'index_condition_pushdown=on';

6.3 查询缓存

sql 复制代码

-- 查看查询缓存状态
SHOW VARIABLES LIKE 'query_cache%';

-- 使用 SQL_CACHE
SELECT SQL_CACHE * FROM students WHERE id = 1;

-- 使用 SQL_NO_CACHE
SELECT SQL_NO_CACHE * FROM large_table;

七、安全管理

7.1 用户权限管理

sql 复制代码

-- 创建用户
CREATE USER 'readonly'@'localhost' IDENTIFIED BY 'password';

-- 授予权限
GRANT SELECT ON school.* TO 'readonly'@'localhost';
GRANT INSERT, UPDATE ON school.students TO 'editor'@'%';
GRANT ALL PRIVILEGES ON *.* TO 'admin'@'localhost' WITH GRANT OPTION;

-- 回收权限
REVOKE INSERT ON school.students FROM 'editor'@'%';
REVOKE ALL PRIVILEGES, GRANT OPTION FROM 'admin'@'localhost';

-- 刷新权限
FLUSH PRIVILEGES;

7.2 数据备份与恢复

sql 复制代码

-- 导出数据（命令行）
mysqldump -u root -p school > school_backup.sql

-- 导入数据
mysql -u root -p school < school_backup.sql

-- 导出特定表
mysqldump -u root -p school students courses > tables_backup.sql