MySQL SQL基础练习100题：从入门到实战-代码聚汇网

MySQL SQL基础练习100题：从入门到实战

不贪吃·2026-08-16·阅读 22 GEO检测（免费）

MySQLSQL练习数据库查询

|难度：普通|阅读约 54 分钟

1. MySQL SQL基础练习的必要性

对于任何想从事数据库相关工作或提升数据处理能力的人来说，MySQL SQL基础练习都是必经之路。我见过太多人把"会写SQL"挂在嘴边，但面对实际业务需求时却无从下手。基础不牢，地动山摇——这句话在SQL学习上体现得尤为明显。

为什么100道基础练习题如此重要？因为SQL的复杂性不在于语法本身，而在于如何将业务需求准确转化为查询逻辑。这100道题就像围棋中的定式，通过反复练习能培养出对数据关系的直觉判断。我在带团队时发现，那些能快速解决复杂查询问题的人，无一例外都有扎实的基础练习功底。

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2. 环境准备与数据初始化

2.1 MySQL安装配置要点

虽然题目是练习题，但真实的操作环境能极大提升学习效果。推荐使用MySQL 8.0+版本，它在窗口函数、CTE等现代SQL特性上支持更好。安装时注意：

bash复制# Ubuntu安装示例
sudo apt update
sudo apt install mysql-server
sudo mysql_secure_installation

Windows用户可以从MySQL官网下载安装包，安装时特别注意：

选择"Developer Default"配置
设置root密码复杂度至少8位含大小写和特殊字符
端口保持默认3306，但生产环境一定要修改

重要提示：安装完成后务必创建专用练习用户，不要直接用root操作：
sql复制CREATE USER 'sql_learner'@'localhost' IDENTIFIED BY 'Practice@123';
GRANT ALL PRIVILEGES ON *.* TO 'sql_learner'@'localhost';
FLUSH PRIVILEGES;

2.2 练习数据库设计

我设计了一套包含6个表的电商数据库模型，覆盖了SQL练习所需的各种场景：

sql复制CREATE DATABASE sql_practice;
USE sql_practice;

-- 用户表
CREATE TABLE users (
    user_id INT PRIMARY KEY AUTO_INCREMENT,
    username VARCHAR(50) NOT NULL UNIQUE,
    email VARCHAR(100) NOT NULL UNIQUE,
    join_date DATETIME DEFAULT CURRENT_TIMESTAMP,
    vip_level ENUM('普通','白银','黄金','铂金') DEFAULT '普通'
);

-- 商品表
CREATE TABLE products (
    product_id INT PRIMARY KEY AUTO_INCREMENT,
    product_name VARCHAR(100) NOT NULL,
    category_id INT,
    price DECIMAL(10,2) NOT NULL,
    stock INT NOT NULL DEFAULT 0,
    is_active BOOLEAN DEFAULT TRUE
);

-- 订单表（核心练习表）
CREATE TABLE orders (
    order_id INT PRIMARY KEY AUTO_INCREMENT,
    user_id INT NOT NULL,
    order_date DATETIME DEFAULT CURRENT_TIMESTAMP,
    total_amount DECIMAL(12,2),
    status ENUM('待支付','已支付','已发货','已完成','已取消') DEFAULT '待支付',
    FOREIGN KEY (user_id) REFERENCES users(user_id)
);

-- 订单明细表
CREATE TABLE order_items (
    item_id INT PRIMARY KEY AUTO_INCREMENT,
    order_id INT NOT NULL,
    product_id INT NOT NULL,
    quantity INT NOT NULL DEFAULT 1,
    unit_price DECIMAL(10,2) NOT NULL,
    FOREIGN KEY (order_id) REFERENCES orders(order_id),
    FOREIGN KEY (product_id) REFERENCES products(product_id)
);

-- 商品分类表
CREATE TABLE categories (
    category_id INT PRIMARY KEY AUTO_INCREMENT,
    category_name VARCHAR(50) NOT NULL,
    parent_id INT NULL
);

-- 用户地址表
CREATE TABLE user_addresses (
    address_id INT PRIMARY KEY AUTO_INCREMENT,
    user_id INT NOT NULL,
    is_default BOOLEAN DEFAULT FALSE,
    province VARCHAR(50),
    city VARCHAR(50),
    district VARCHAR(50),
    detail_address VARCHAR(200),
    FOREIGN KEY (user_id) REFERENCES users(user_id)
);

这套模型包含了：

基础CRUD操作
多表关联查询
聚合函数使用
子查询应用
事务处理场景
复杂业务逻辑实现

3. 基础查询专项训练

3.1 单表查询核心20题

查询所有商品信息（基础SELECT）

sql复制SELECT * FROM products;

查询活跃商品（WHERE条件）

sql复制SELECT product_name, price 
FROM products 
WHERE is_active = TRUE;

查询价格区间商品（BETWEEN）

sql复制SELECT product_name, price
FROM products
WHERE price BETWEEN 50 AND 200;

查询特定分类商品（IN操作符）

sql复制SELECT product_name, category_id
FROM products
WHERE category_id IN (1,3,5);

模糊查询商品名（LIKE）

sql复制SELECT product_name
FROM products
WHERE product_name LIKE '%手机%';

查询结果排序（ORDER BY）

sql复制SELECT product_name, price
FROM products
ORDER BY price DESC, product_name ASC;

分页查询（LIMIT）

sql复制SELECT product_name, price
FROM products
ORDER BY price DESC
LIMIT 10 OFFSET 20;  -- 第三页，每页10条

去重查询（DISTINCT）

sql复制SELECT DISTINCT category_id
FROM products;

列别名使用（AS）

sql复制SELECT 
    product_name AS '商品名称',
    price AS '价格'
FROM products;

条件组合查询（AND/OR）

sql复制SELECT product_name, price, stock
FROM products
WHERE (price > 100 OR stock < 50) 
AND is_active = TRUE;

3.2 聚合函数深度练习

统计商品总数（COUNT）

sql复制SELECT COUNT(*) AS total_products
FROM products;

计算平均价格（AVG）

sql复制SELECT AVG(price) AS avg_price
FROM products
WHERE is_active = TRUE;

最高/最低价商品（MAX/MIN）

sql复制SELECT 
    MAX(price) AS max_price,
    MIN(price) AS min_price
FROM products;

库存总量（SUM）

sql复制SELECT SUM(stock) AS total_stock
FROM products;

分组统计（GROUP BY）

sql复制SELECT 
    category_id,
    COUNT(*) AS product_count,
    AVG(price) AS avg_price
FROM products
GROUP BY category_id;

分组后过滤（HAVING）

sql复制SELECT 
    category_id,
    COUNT(*) AS product_count
FROM products
GROUP BY category_id
HAVING COUNT(*) > 5;

多列分组

sql复制SELECT 
    category_id,
    is_active,
    COUNT(*) AS count
FROM products
GROUP BY category_id, is_active;

分组后排序

sql复制SELECT 
    category_id,
    AVG(price) AS avg_price
FROM products
GROUP BY category_id
ORDER BY avg_price DESC;

条件计数（COUNT+IF）

sql复制SELECT 
    COUNT(*) AS total,
    COUNT(IF(price>100,1,NULL)) AS high_price_count
FROM products;

分组拼接字符串（GROUP_CONCAT）

sql复制SELECT 
    category_id,
    GROUP_CONCAT(product_name SEPARATOR '|') AS products
FROM products
GROUP BY category_id;

4. 多表关联查询实战

4.1 连接查询基础

内连接查询（INNER JOIN）

sql复制SELECT 
    p.product_name,
    c.category_name
FROM products p
INNER JOIN categories c ON p.category_id = c.category_id;

左外连接（LEFT JOIN）

sql复制SELECT 
    u.username,
    o.order_id
FROM users u
LEFT JOIN orders o ON u.user_id = o.user_id;

右外连接（RIGHT JOIN）

sql复制SELECT 
    o.order_id,
    a.province
FROM orders o
RIGHT JOIN user_addresses a ON o.user_id = a.user_id;

全外连接模拟（UNION）

sql复制SELECT u.user_id, o.order_id
FROM users u
LEFT JOIN orders o ON u.user_id = o.user_id
UNION
SELECT u.user_id, o.order_id
FROM users u
RIGHT JOIN orders o ON u.user_id = o.user_id
WHERE u.user_id IS NULL;

自连接查询（同一表连接）

sql复制SELECT 
    c1.category_name,
    c2.category_name AS parent_category
FROM categories c1
LEFT JOIN categories c2 ON c1.parent_id = c2.category_id;

4.2 复杂关联查询

多表连接

sql复制SELECT 
    u.username,
    o.order_id,
    p.product_name,
    oi.quantity
FROM users u
JOIN orders o ON u.user_id = o.user_id
JOIN order_items oi ON o.order_id = oi.order_id
JOIN products p ON oi.product_id = p.product_id;

连接过滤条件

sql复制SELECT 
    p.product_name,
    oi.quantity,
    o.order_date
FROM products p
JOIN order_items oi ON p.product_id = oi.product_id
JOIN orders o ON oi.order_id = o.order_id
WHERE o.order_date > '2023-01-01'
AND p.category_id = 3;

连接+聚合组合

sql复制SELECT 
    c.category_name,
    COUNT(oi.item_id) AS sales_count,
    SUM(oi.quantity * oi.unit_price) AS total_sales
FROM categories c
LEFT JOIN products p ON c.category_id = p.category_id
LEFT JOIN order_items oi ON p.product_id = oi.product_id
GROUP BY c.category_id;

不等值连接

sql复制SELECT 
    p1.product_name AS product1,
    p2.product_name AS product2
FROM products p1
JOIN products p2 ON p1.price > p2.price * 2;

自然连接（不推荐生产环境使用）

sql复制SELECT 
    u.username,
    o.order_id
FROM users u
NATURAL JOIN orders o;

5. 子查询与高级特性

5.1 子查询应用

WHERE子查询

sql复制SELECT product_name, price
FROM products
WHERE price > (SELECT AVG(price) FROM products);

IN子查询

sql复制SELECT username
FROM users
WHERE user_id IN (
    SELECT DISTINCT user_id 
    FROM orders 
    WHERE total_amount > 1000
);

EXISTS子查询

sql复制SELECT c.category_name
FROM categories c
WHERE EXISTS (
    SELECT 1 
    FROM products p 
    WHERE p.category_id = c.category_id
    AND p.stock < 10
);

FROM子句子查询

sql复制SELECT 
    avg_stats.category_id,
    avg_stats.avg_price
FROM (
    SELECT 
        category_id,
        AVG(price) AS avg_price
    FROM products
    GROUP BY category_id
) AS avg_stats
WHERE avg_stats.avg_price > 150;

关联子查询

sql复制SELECT 
    p1.product_name,
    p1.price
FROM products p1
WHERE p1.price > (
    SELECT AVG(p2.price)
    FROM products p2
    WHERE p2.category_id = p1.category_id
);

5.2 高级查询技术

公用表表达式(CTE)

sql复制WITH high_value_orders AS (
    SELECT order_id, total_amount
    FROM orders
    WHERE total_amount > 500
)
SELECT 
    u.username,
    hvo.total_amount
FROM users u
JOIN high_value_orders hvo ON u.user_id = hvo.user_id;

递归CTE（查询分类层级）

sql复制WITH RECURSIVE category_tree AS (
    -- 基础查询：顶级分类
    SELECT category_id, category_name, parent_id, 1 AS level
    FROM categories
    WHERE parent_id IS NULL
    
    UNION ALL
    
    -- 递归查询：子分类
    SELECT c.category_id, c.category_name, c.parent_id, ct.level + 1
    FROM categories c
    JOIN category_tree ct ON c.parent_id = ct.category_id
)
SELECT * FROM category_tree
ORDER BY level, category_id;

窗口函数（ROW_NUMBER）

sql复制SELECT 
    product_name,
    price,
    ROW_NUMBER() OVER (ORDER BY price DESC) AS price_rank
FROM products;

窗口函数（PARTITION BY）

sql复制SELECT 
    category_id,
    product_name,
    price,
    RANK() OVER (PARTITION BY category_id ORDER BY price DESC) AS price_rank_in_category
FROM products;

累计计算（SUM OVER）

sql复制SELECT 
    order_date,
    total_amount,
    SUM(total_amount) OVER (ORDER BY order_date) AS running_total
FROM orders;

6. 数据修改与事务控制

6.1 数据操作语言(DML)

插入单条记录

sql复制INSERT INTO products (product_name, category_id, price, stock)
VALUES ('无线蓝牙耳机', 5, 299.00, 100);

批量插入数据

sql复制INSERT INTO products (product_name, category_id, price, stock)
VALUES 
    ('智能手表', 3, 899.00, 50),
    ('平板电脑', 3, 1999.00, 30),
    ('机械键盘', 4, 399.00, 80);

插入查询结果

sql复制INSERT INTO product_archive (product_id, product_name, price)
SELECT product_id, product_name, price
FROM products
WHERE is_active = FALSE;

更新单列数据

sql复制UPDATE products
SET price = price * 0.9  -- 打9折
WHERE category_id = 3;

条件更新多列

sql复制UPDATE users
SET 
    vip_level = '黄金',
    email = CONCAT('gold_', email)
WHERE user_id IN (
    SELECT user_id
    FROM orders
    GROUP BY user_id
    HAVING SUM(total_amount) > 5000
);

删除特定记录

sql复制DELETE FROM products
WHERE stock = 0
AND is_active = FALSE;

清空表数据

sql复制TRUNCATE TABLE temp_orders;

6.2 事务控制实战

基本事务流程

sql复制START TRANSACTION;

UPDATE accounts SET balance = balance - 500 WHERE user_id = 1001;
UPDATE accounts SET balance = balance + 500 WHERE user_id = 1002;

-- 检查是否有错误
IF @@ERROR_COUNT = 0 THEN
    COMMIT;
ELSE
    ROLLBACK;
END IF;

保存点使用

sql复制START TRANSACTION;

INSERT INTO orders (user_id, total_amount) VALUES (101, 1200);
SAVEPOINT order_created;

UPDATE products SET stock = stock - 1 WHERE product_id = 5;
-- 假设这里库存不足导致失败

ROLLBACK TO SAVEPOINT order_created;
-- 可以尝试其他操作或取消订单

COMMIT;

事务隔离级别设置

sql复制SET TRANSACTION ISOLATION LEVEL READ COMMITTED;
START TRANSACTION;
-- 执行查询
COMMIT;

7. 视图与存储过程

7.1 视图创建与应用

创建简单视图

sql复制CREATE VIEW active_products_view AS
SELECT product_id, product_name, price
FROM products
WHERE is_active = TRUE;

使用视图查询

sql复制SELECT * FROM active_products_view
WHERE price < 100;

创建连接视图

sql复制CREATE VIEW order_detail_view AS
SELECT 
    o.order_id,
    u.username,
    o.order_date,
    oi.product_id,
    p.product_name,
    oi.quantity,
    oi.unit_price
FROM orders o
JOIN users u ON o.user_id = u.user_id
JOIN order_items oi ON o.order_id = oi.order_id
JOIN products p ON oi.product_id = p.product_id;

视图更新限制

sql复制-- 可更新视图示例
CREATE VIEW updatable_products AS
SELECT product_id, product_name, price
FROM products
WHERE category_id = 1
WITH CHECK OPTION;

-- 此更新会成功
UPDATE updatable_products SET price = 99 WHERE product_id = 101;

-- 此更新会失败（违反CHECK OPTION）
UPDATE updatable_products SET category_id = 2 WHERE product_id = 101;

修改和删除视图

sql复制ALTER VIEW active_products_view AS
SELECT product_id, product_name, price, stock
FROM products
WHERE is_active = TRUE AND stock > 0;

DROP VIEW IF EXISTS old_product_view;

7.2 存储过程开发

创建基础存储过程

sql复制DELIMITER //
CREATE PROCEDURE get_user_orders(IN user_id INT)
BEGIN
    SELECT * FROM orders WHERE user_id = user_id;
END //
DELIMITER ;

-- 调用
CALL get_user_orders(101);

带输出参数的存储过程

sql复制DELIMITER //
CREATE PROCEDURE get_order_stats(
    IN user_id INT,
    OUT total_orders INT,
    OUT total_amount DECIMAL(12,2)
)
BEGIN
    SELECT COUNT(*), SUM(total_amount)
    INTO total_orders, total_amount
    FROM orders
    WHERE user_id = user_id;
END //
DELIMITER ;

-- 调用
CALL get_order_stats(101, @order_count, @order_total);
SELECT @order_count, @order_total;

条件逻辑存储过程

sql复制DELIMITER //
CREATE PROCEDURE update_product_price(
    IN product_id INT,
    IN increase_percent DECIMAL(5,2)
)
BEGIN
    DECLARE current_price DECIMAL(10,2);
    
    SELECT price INTO current_price FROM products WHERE product_id = product_id;
    
    IF current_price * (1 + increase_percent/100) > 1000 THEN
        SIGNAL SQLSTATE '45000' 
        SET MESSAGE_TEXT = 'Price cannot exceed 1000 after increase';
    ELSE
        UPDATE products 
        SET price = price * (1 + increase_percent/100)
        WHERE product_id = product_id;
    END IF;
END //
DELIMITER ;

循环处理存储过程

sql复制DELIMITER //
CREATE PROCEDURE apply_discount_to_category(
    IN category_id INT,
    IN discount_percent DECIMAL(5,2)
)
BEGIN
    DECLARE done INT DEFAULT FALSE;
    DECLARE p_id INT;
    DECLARE cur CURSOR FOR 
        SELECT product_id FROM products WHERE category_id = category_id;
    DECLARE CONTINUE HANDLER FOR NOT FOUND SET done = TRUE;
    
    OPEN cur;
    
    read_loop: LOOP
        FETCH cur INTO p_id;
        IF done THEN
            LEAVE read_loop;
        END IF;
        
        UPDATE products
        SET price = price * (1 - discount_percent/100)
        WHERE product_id = p_id;
    END LOOP;
    
    CLOSE cur;
END //
DELIMITER ;

错误处理存储过程

sql复制DELIMITER //
CREATE PROCEDURE safe_delete_product(
    IN product_id INT
)
BEGIN
    DECLARE EXIT HANDLER FOR SQLEXCEPTION
    BEGIN
        ROLLBACK;
        SELECT 'Error occurred - transaction rolled back' AS message;
    END;
    
    START TRANSACTION;
    
    -- 检查是否有订单关联
    IF EXISTS (SELECT 1 FROM order_items WHERE product_id = product_id) THEN
        SIGNAL SQLSTATE '45000' 
        SET MESSAGE_TEXT = 'Cannot delete product with existing orders';
    END IF;
    
    -- 删除操作
    DELETE FROM products WHERE product_id = product_id;
    
    COMMIT;
    SELECT 'Product deleted successfully' AS message;
END //
DELIMITER ;

8. 索引与性能优化

8.1 索引创建与使用

创建单列索引

sql复制CREATE INDEX idx_product_name ON products(product_name);

创建复合索引

sql复制CREATE INDEX idx_category_price ON products(category_id, price);

唯一索引

sql复制CREATE UNIQUE INDEX idx_unique_email ON users(email);

查看表索引

sql复制SHOW INDEX FROM products;

删除索引

sql复制DROP INDEX idx_product_name ON products;

8.2 查询性能分析

使用EXPLAIN分析查询

sql复制EXPLAIN SELECT * FROM orders WHERE user_id = 101;

分析索引使用情况

sql复制EXPLAIN FORMAT=JSON
SELECT p.product_name, COUNT(oi.item_id)
FROM products p
LEFT JOIN order_items oi ON p.product_id = oi.product_id
GROUP BY p.product_id;

识别全表扫描

sql复制-- 检查Extra列中的"Using where; Using filesort"等提示
EXPLAIN SELECT * FROM products WHERE price > 100 ORDER BY product_name;

强制使用索引

sql复制SELECT * FROM products FORCE INDEX (idx_category_price)
WHERE category_id = 3 AND price > 100;

忽略索引

sql复制SELECT * FROM products IGNORE INDEX (idx_category_price)
WHERE category_id = 3;

9. 高级特性与技巧

9.1 JSON数据处理

创建JSON列

sql复制ALTER TABLE products ADD COLUMN specs JSON;

插入JSON数据

sql复制UPDATE products 
SET specs = '{
    "color": "black",
    "weight": "350g",
    "dimensions": {
        "length": 15,
        "width": 8,
        "height": 1
    }
}'
WHERE product_id = 101;

查询JSON字段

sql复制SELECT 
    product_name,
    specs->>"$.color" AS color,
    specs->>"$.dimensions.length" AS length
FROM products;

JSON路径查询

sql复制SELECT 
    product_name,
    JSON_EXTRACT(specs, '$.dimensions.width') AS width
FROM products
WHERE specs->>"$.color" = 'black';

修改JSON数据

sql复制UPDATE products
SET specs = JSON_SET(specs, '$.color', 'blue')
WHERE product_id = 101;

9.2 正则表达式应用

正则匹配查询

sql复制SELECT username FROM users
WHERE username REGEXP '^[a-z]{2}[0-9]{4}$';

正则替换

sql复制UPDATE users
SET email = REGEXP_REPLACE(email, '@olddomain.com$', '@newdomain.com')
WHERE email REGEXP '@olddomain.com$';

提取字符串部分

sql复制SELECT 
    product_name,
    REGEXP_SUBSTR(product_name, '[A-Z]{2,3}[0-9]{4}') AS model_number
FROM products
WHERE product_name REGEXP '[A-Z]{2,3}[0-9]{4}';

复杂正则验证

sql复制SELECT email FROM users
WHERE email REGEXP '^[A-Za-z0-9._%-]+@[A-Za-z0-9.-]+\\.[A-Za-z]{2,4}$';

正则分组提取

sql复制SELECT 
    product_name,
    REGEXP_REPLACE(
        product_name,
        '([0-9]{4})([A-Z]{2})',
        '\\1-\\2'
    ) AS formatted_code
FROM products
WHERE product_name REGEXP '[0-9]{4}[A-Z]{2}';

10. 实战综合练习

10.1 电商业务场景

查询每个用户的订单总数和总金额

sql复制SELECT 
    u.user_id,
    u.username,
    COUNT(o.order_id) AS order_count,
    SUM(o.total_amount) AS total_spent
FROM users u
LEFT JOIN orders o ON u.user_id = o.user_id
GROUP BY u.user_id;

查询热销商品TOP10

sql复制SELECT 
    p.product_id,
    p.product_name,
    SUM(oi.quantity) AS total_sold
FROM products p
JOIN order_items oi ON p.product_id = oi.product_id
GROUP BY p.product_id
ORDER BY total_sold DESC
LIMIT 10;

查询有购买但最近30天未登录的用户

sql复制SELECT DISTINCT u.user_id, u.username
FROM users u
JOIN orders o ON u.user_id = o.user_id
WHERE u.last_login < DATE_SUB(NOW(), INTERVAL 30 DAY)
AND o.order_date > DATE_SUB(NOW(), INTERVAL 30 DAY);

查询每个分类的销售额占比

sql复制SELECT 
    c.category_name,
    SUM(oi.quantity * oi.unit_price) AS category_sales,
    SUM(oi.quantity * oi.unit_price) / 
        (SELECT SUM(quantity * unit_price) FROM order_items) * 100 AS percentage
FROM categories c
JOIN products p ON c.category_id = p.category_id
JOIN order_items oi ON p.product_id = oi.product_id
GROUP BY c.category_id
ORDER BY category_sales DESC;

查询有跨分类购买行为的用户

sql复制SELECT DISTINCT u.user_id, u.username
FROM users u
WHERE (
    SELECT COUNT(DISTINCT p.category_id)
    FROM orders o
    JOIN order_items oi ON o.order_id = oi.order_id
    JOIN products p ON oi.product_id = p.product_id
    WHERE o.user_id = u.user_id
) > 1;

10.2 复杂分析场景

查询连续3天有登录的用户

sql复制WITH user_login_dates AS (
    SELECT 
        user_id,
        DATE(login_time) AS login_date,
        LAG(DATE(login_time), 2) OVER (PARTITION BY user_id ORDER BY login_time) AS prev_prev_date
    FROM user_logins
)
SELECT DISTINCT user_id
FROM user_login_dates
WHERE DATEDIFF(login_date, prev_prev_date) = 2;

计算用户购买频率

sql复制SELECT 
    user_id,
    COUNT(*) AS total_orders,
    DATEDIFF(MAX(order_date), MIN(order_date)) AS days_active,
    COUNT(*) / NULLIF(DATEDIFF(MAX(order_date), MIN(order_date)), 0) * 30 AS orders_per_month
FROM orders
GROUP BY user_id
HAVING COUNT(*) > 1;

查询有升级潜力的用户（差X元升级）

sql复制SELECT 
    u.user_id,
    u.username,
    u.vip_level,
    SUM(o.total_amount) AS total_spent,
    CASE u.vip_level
        WHEN '普通' THEN 1000 - SUM(o.total_amount)
        WHEN '白银' THEN 3000 - SUM(o.total_amount)
        WHEN '黄金' THEN 8000 - SUM(o.total_amount)
        ELSE NULL
    END AS needed_for_next_level
FROM users u
JOIN orders o ON u.user_id = o.user_id
WHERE u.vip_level IN ('普通','白银','黄金')
GROUP BY u.user_id
HAVING needed_for_next_level > 0
ORDER BY needed_for_next_level;

使用交叉表查询每月销售统计

sql复制SELECT 
    YEAR(order_date) AS year,
    SUM(IF(MONTH(order_date)=1, total_amount, 0)) AS Jan,
    SUM(IF(MONTH(order_date)=2, total_amount, 0)) AS Feb,
    SUM(IF(MONTH(order_date)=3, total_amount, 0)) AS Mar,
    -- 其他月份类似
    SUM(total_amount) AS yearly_total
FROM orders
GROUP BY YEAR(order_date)
ORDER BY year;

查询有相似购买行为的用户对

sql复制SELECT 
    u1.user_id AS user1,
    u2.user_id AS user2,
    COUNT(DISTINCT oi1.product_id) AS common_products
FROM users u1
JOIN orders o1 ON u1.user_id = o1.user_id
JOIN order_items oi1 ON o1.order_id = oi1.order_id
JOIN order_items oi2 ON oi1.product_id = oi2.product_id
JOIN orders o2 ON oi2.order_id = o2.order_id
JOIN users u2 ON o2.user_id = u2.user_id
WHERE u1.user_id < u2.user_id
GROUP BY u1.user_id, u2.user_id
HAVING COUNT(DISTINCT oi1.product_id) > 3
ORDER BY common_products DESC;

11. 性能优化实战

11.1 慢查询优化案例

优化分组统计查询

sql复制-- 原始慢查询
SELECT 
    c.category_name,
    COUNT(oi.item_id) AS sales_count
FROM categories c
LEFT JOIN products p ON c.category_id = p.category_id
LEFT JOIN order_items oi ON p.product_id = oi.product_id
GROUP BY c.category_id;

-- 优化方案1：添加索引
ALTER TABLE order_items ADD INDEX idx_product_id (product_id);

-- 优化方案2：使用子查询减少连接
SELECT 
    c.category_name,
    (SELECT COUNT(*) 
     FROM order_items oi 
     JOIN products p ON oi.product_id = p.product_id
     WHERE p.category_id = c.category_id) AS sales_count
FROM categories c;

优化分页查询

sql复制-- 原始慢分页
SELECT * FROM orders
ORDER BY order_date DESC
LIMIT 10000, 20;

-- 优化方案1：使用索引覆盖
SELECT o.* FROM orders o
JOIN (
    SELECT order_id FROM orders
    ORDER BY order_date DESC
    LIMIT 10000, 20
) AS tmp ON o.order_id = tmp.order_id;

-- 优化方案2：使用游标分页
SELECT * FROM orders
WHERE order_date < '2023-06-01'
ORDER BY order_date DESC
LIMIT 20;

11.2 执行计划分析

分析复杂连接查询

sql复制EXPLAIN 
SELECT 
    u.username,
    p.product_name,
    COUNT(oi.item_id) AS purchase_count
FROM users u
JOIN orders o ON u.user_id = o.user_id
JOIN order_items oi ON o.order_id = oi.order_id
JOIN products p ON oi.product_id = p.product_id
GROUP BY u.user_id, p.product_id;

识别全表扫描

sql复制-- 检查type列是否为ALL
EXPLAIN SELECT * FROM products WHERE product_name LIKE '%Pro%';

优化排序操作

sql复制-- 检查Extra列是否有"Using filesort"
EXPLAIN SELECT * FROM products ORDER BY category_id, price DESC;

-- 添加复合索引
ALTER TABLE products ADD INDEX idx_category_price (category_id, price DESC);

12. 安全与维护

12.1 数据备份与恢复

使用mysqldump备份

bash复制mysqldump -u username -p sql_practice > sql_practice_backup.sql

恢复数据库

bash复制mysql -u username -p sql_practice < sql_practice_backup.sql

12.2 用户权限管理

创建只读用户

sql复制CREATE USER 'report_user'@'%' IDENTIFIED BY 'ReadOnly@123';
GRANT SELECT ON sql_practice.* TO 'report_user'@'%';

权限回收

sql复制REVOKE ALL PRIVILEGES ON *.* FROM 'old_user'@'localhost';

查看用户权限

sql复制SHOW GRANTS FOR 'current_user'@'localhost';

13. 持续学习建议

完成这100道基础练习题后，建议从以下几个方向继续深入学习：

研究MySQL官方文档中的高级特性，如窗口函数、CTE、JSON处理等
学习查询优化技巧，掌握EXPLAIN执行计划分析
实践复杂业务场景的SQL实现，如漏斗分析、留存计算等
了解MySQL的架构原理，包括存储引擎、索引实现、事务隔离等
探索其他数据库系统如PostgreSQL的特性对比

我在实际工作中发现，SQL能力的提升关键在于持续实践和反思。建议定期回顾这些基础题目，随着经验增长，你会对相同的题目有更深层次的理解。当你能轻松解决90%以上题目时，就可以开始挑战更复杂的业务分析场景了。