【MYSQL】第二篇：SQL进阶指南：增删改查与性能优化实战手册

第二篇：SQL进阶指南：增删改查与性能优化实战手册

掌握了SQL基础查询后，是时候深入数据库操作的核心了！本文将完整介绍所有数据操作函数、索引函数、多表关联函数和统计函数，让您从SQL使用者升级为数据库管理者。

核心内容

1. 数据操作完整函数集

INSERT 语句 - 插入数据

-- 插入单条完整记录
INSERT INTO users VALUES (1, '张三', '[e-mail]', '2024-01-01');-- 插入指定字段（推荐）
INSERT INTO users (username, email, age) VALUES ('李四', '[e-mail]', 30);-- 批量插入
INSERT INTO products (name, price) VALUES 
('iPhone', 5999),
('iPad', 3299),
('MacBook', 9999);-- 从查询结果插入
INSERT INTO user_backup 
SELECT * FROM users WHERE created_at < '2023-01-01';

作用：向表中插入新记录

UPDATE 语句 - 更新数据

-- 更新单个字段
UPDATE users SET email = '[e-mail]' WHERE id = 1;-- 更新多个字段
UPDATE products 
SET price = price * 0.9, update_time = NOW(),discount = 1
WHERE category = '电子产品';-- 基于条件更新
UPDATE orders 
SET status = 'completed'
WHERE status = 'pending' AND created_at < '2024-01-01';-- 使用表达式更新
UPDATE accounts 
SET balance = balance + 1000 
WHERE user_id = 123;

作用：修改表中的现有记录

DELETE 语句 - 删除数据

-- 删除特定记录
DELETE FROM orders WHERE status = 'cancelled';-- 删除过期数据
DELETE FROM user_sessions WHERE expire_time < NOW();-- 使用子查询删除
DELETE FROM users 
WHERE id IN (SELECT user_id FROM inactive_users);

作用：从表中删除记录

TRUNCATE TABLE 语句

-- 清空整个表
TRUNCATE TABLE temp_logs;-- 与DELETE的区别
-- DELETE: 逐行删除，可恢复，记录日志
-- TRUNCATE: 立即清空，不可恢复，不记录日志

作用：快速清空整个表

2. 索引相关完整函数

CREATE INDEX - 创建索引

-- 创建普通索引
CREATE INDEX idx_user_email ON users(email);-- 创建唯一索引
CREATE UNIQUE INDEX idx_unique_username ON users(username);-- 创建复合索引
CREATE INDEX idx_category_price ON products(category_id, price);-- 创建聚簇索引
CREATE CLUSTERED INDEX idx_user_clustered ON users(id);-- 创建允许重复的聚簇索引
CREATE CLUSTERED INDEX idx_user_dup ON users(department) 
WITH ALLOW_DUP_ROW;

作用：创建索引以提高查询性能

DROP INDEX - 删除索引

-- 删除索引
DROP INDEX idx_user_email ON users;-- 删除复合索引
DROP INDEX idx_category_price ON products;

作用：删除不再需要的索引

3. 多表关联完整函数

INNER JOIN - 内连接

-- 基本内连接
SELECT o.order_id, u.username
FROM orders o
INNER JOIN users u ON o.user_id = u.id;-- 多表内连接
SELECT o.order_id, u.username, p.product_name
FROM orders o
INNER JOIN users u ON o.user_id = u.id
INNER JOIN products p ON o.product_id = p.id;

作用：返回两个表中匹配的记录

LEFT JOIN / RIGHT JOIN - 外连接

-- 左外连接（返回左表所有记录）
SELECT u.username, o.order_id
FROM users u
LEFT JOIN orders o ON u.id = o.user_id;-- 右外连接（返回右表所有记录）
SELECT u.username, o.order_id
FROM orders o
RIGHT JOIN users u ON o.user_id = u.id;-- 完整外连接（MySQL不支持，可用UNION实现）
SELECT u.username, o.order_id
FROM users u
LEFT JOIN orders o ON u.id = o.user_id
UNION
SELECT u.username, o.order_id
FROM users u
RIGHT JOIN orders o ON u.id = o.user_id;

作用：返回一个表的所有记录和另一个表的匹配记录

自连接

-- 员工和经理关系
SELECT e.name as employee_name,m.name as manager_name
FROM employees e
LEFT JOIN employees m ON e.manager_id = m.id;

作用：表与自身进行连接

4. 聚合统计完整函数

GROUP BY - 分组统计

-- 按城市分组统计
SELECT city, COUNT(*) as user_count
FROM users
GROUP BY city;-- 多字段分组
SELECT department, gender, COUNT(*) as count
FROM employees
GROUP BY department, gender;-- 分组后使用聚合函数
SELECT category,COUNT(*) as product_count,AVG(price) as avg_price,MAX(price) as max_price,MIN(price) as min_price,SUM(stock) as total_stock
FROM products
GROUP BY category;

作用：按指定字段对结果进行分组

HAVING - 分组后过滤

-- 过滤分组结果
SELECT city, COUNT(*) as user_count
FROM users
GROUP BY city
HAVING COUNT(*) > 100;-- 多个条件过滤
SELECT category, AVG(price) as avg_price
FROM products
GROUP BY category
HAVING AVG(price) > 100 AND COUNT(*) > 10;-- 使用聚合函数条件
SELECT user_id, SUM(amount) as total_spent
FROM orders
GROUP BY user_id
HAVING SUM(amount) > 1000;

作用：对分组后的结果进行条件过滤

完整的聚合函数集

COUNT() - 计数函数

-- 统计总记录数
SELECT COUNT(*) FROM users;-- 统计非空值数量
SELECT COUNT(email) FROM users;-- 统计不同值的数量
SELECT COUNT(DISTINCT city) FROM users;-- 分组计数
SELECT department, COUNT(*) FROM employees GROUP BY department;

SUM() - 求和函数

-- 计算总和
SELECT SUM(amount) FROM orders;-- 分组求和
SELECT user_id, SUM(amount) FROM orders GROUP BY user_id;-- 条件求和
SELECT SUM(CASE WHEN status='completed' THEN amount ELSE 0 END) 
FROM orders;

AVG() - 平均值函数

-- 计算平均值
SELECT AVG(price) FROM products;-- 分组平均值
SELECT category, AVG(price) FROM products GROUP BY category;-- 忽略空值的平均值
SELECT AVG(COALESCE(age, 0)) FROM users;

MAX() / MIN() - 极值函数

-- 最大值和最小值
SELECT MAX(price), MIN(price) FROM products;-- 分组极值
SELECT category, MAX(price), MIN(price) FROM products GROUP BY category;-- 日期极值
SELECT MAX(created_at), MIN(created_at) FROM users;

5. 子查询完整函数

标量子查询

-- 返回单个值的子查询
SELECT name, price 
FROM products 
WHERE price > (SELECT AVG(price) FROM products);-- 在SELECT中使用
SELECT name,price,(SELECT AVG(price) FROM products) as avg_price
FROM products;

EXISTS 子查询

-- 检查是否存在相关记录
SELECT username
FROM users u
WHERE EXISTS (SELECT 1 FROM orders o WHERE o.user_id = u.id);-- 不存在相关记录
SELECT username
FROM users u
WHERE NOT EXISTS (SELECT 1 FROM orders o WHERE o.user_id = u.id);

IN 子查询

-- 使用IN的子查询
SELECT * FROM users 
WHERE id IN (SELECT user_id FROM orders WHERE amount > 1000);-- 多值IN查询
SELECT * FROM products 
WHERE category IN (SELECT category FROM categories WHERE active = 1);

6. 高级比较函数

BETWEEN - 范围查询

-- 数值范围
SELECT * FROM products WHERE price BETWEEN 100 AND 500;-- 日期范围
SELECT * FROM orders 
WHERE order_date BETWEEN '2024-01-01' AND '2024-01-31';-- 不在范围内
SELECT * FROM products WHERE price NOT BETWEEN 100 AND 500;

作用：查询在某个范围内的值

IN - 多值匹配

-- 匹配多个值
SELECT * FROM users WHERE city IN ('北京', '上海', '广州');-- 子查询IN
SELECT * FROM products 
WHERE category_id IN (SELECT id FROM categories WHERE type = 'electronic');-- 不匹配多个值
SELECT * FROM users WHERE city NOT IN ('北京', '上海');

作用：查询匹配多个值中的任何一个

7. 完整实战：电商数据分析系统

-- 1. 用户购买行为分析
SELECT u.id,u.username,u.city,COUNT(o.id) as order_count,SUM(o.amount) as total_spent,AVG(o.amount) as avg_order_value,MAX(o.created_at) as last_order_date,DATEDIFF(NOW(), MAX(o.created_at)) as days_since_last_order
FROM users u
LEFT JOIN orders o ON u.id = o.user_id
WHERE o.status = 'completed'
GROUP BY u.id, u.username, u.city
HAVING COUNT(o.id) >= 1
ORDER BY total_spent DESC;-- 2. 商品销售排行榜
SELECT p.id,p.name,p.category,SUM(oi.quantity) as total_sold,SUM(oi.quantity * oi.price) as total_revenue,COUNT(DISTINCT o.user_id) as unique_customers,AVG(oi.quantity) as avg_quantity_per_order
FROM products p
INNER JOIN order_items oi ON p.id = oi.product_id
INNER JOIN orders o ON oi.order_id = o.id
WHERE o.status = 'completed'AND o.created_at BETWEEN '2024-01-01' AND '2024-12-31'
GROUP BY p.id, p.name, p.category
HAVING total_sold > 0
ORDER BY total_revenue DESC
LIMIT 20;-- 3. 月度销售趋势分析
SELECT YEAR(created_at) as year,MONTH(created_at) as month,COUNT(*) as order_count,SUM(amount) as monthly_revenue,AVG(amount) as avg_order_value,COUNT(DISTINCT user_id) as active_customers
FROM orders
WHERE status = 'completed'AND created_at >= '2023-01-01'
GROUP BY YEAR(created_at), MONTH(created_at)
ORDER BY year DESC, month DESC;

8. 性能优化相关函数

EXPLAIN - 执行计划分析

-- 查看查询执行计划
EXPLAIN SELECT * FROM users WHERE email = '[e-mail]';-- 详细执行计划
EXPLAIN FORMAT=JSON SELECT * FROM users WHERE age > 18;-- 分析多表查询
EXPLAIN 
SELECT u.username, o.order_id 
FROM users u 
INNER JOIN orders o ON u.id = o.user_id;

作用：显示MySQL如何执行查询

SHOW INDEX - 查看索引

-- 查看表的索引
SHOW INDEX FROM users;-- 查看索引详细信息
SHOW INDEX FROM users WHERE Key_name = 'idx_user_email';

作用：显示表的索引信息

本篇涵盖的所有函数总结

函数/语句	作用	语法示例
INSERT	插入数据	INSERT INTO table VALUES (...)
UPDATE	更新数据	UPDATE table SET column=value WHERE condition
DELETE	删除数据	DELETE FROM table WHERE condition
TRUNCATE	清空表	TRUNCATE TABLE table
CREATE INDEX	创建索引	CREATE INDEX idx_name ON table(column)
DROP INDEX	删除索引	DROP INDEX idx_name ON table
INNER JOIN	内连接	SELECT * FROM a INNER JOIN b ON a.id=b.id
LEFT JOIN	左外连接	SELECT * FROM a LEFT JOIN b ON a.id=b.id
RIGHT JOIN	右外连接	SELECT * FROM a RIGHT JOIN b ON a.id=b.id
GROUP BY	分组统计	SELECT column FROM table GROUP BY column
HAVING	分组过滤	GROUP BY column HAVING condition
COUNT()	计数	SELECT COUNT(column) FROM table
SUM()	求和	SELECT SUM(column) FROM table
AVG()	平均值	SELECT AVG(column) FROM table
MAX()/MIN()	极值	SELECT MAX(column) FROM table
EXISTS	存在检查	WHERE EXISTS (subquery)
BETWEEN	范围查询	WHERE column BETWEEN value1 AND value2
IN	多值匹配	WHERE column IN (value1, value2)
EXPLAIN	执行计划	EXPLAIN SELECT ...
SHOW INDEX	查看索引	SHOW INDEX FROM table

附基础篇：第一篇：SQL入门宝典：零基础学会数据查询，这一篇就够了！