MySQL DML基本操作示例详解

INSERT INTO table_name (column1, column2, column3, ...)
VALUES (value1, value2, value3, ...);

-- 假设表有 id, name, email, age 列，其中 id 是自增主键
INSERT INTO users (name, email, age)
VALUES ('张三', 'zhangsan@example.com', 25);

-- 只插入 name 和 email，age 使用默认值或 NULL
INSERT INTO users (name, email)
VALUES ('李四', 'lisi@example.com');

INSERT INTO users (name, email, age)
VALUES 
('王五', 'wangwu@example.com', 30),
('赵六', 'zhaoliu@example.com', 28),
('孙七', 'sunqi@example.com', 35);

-- 将临时表中的数据插入到正式表
INSERT INTO users (name, email, age)
SELECT temp_name, temp_email, temp_age FROM temp_users;

-- 如果遇到重复的唯一键（如email），则更新其他字段
INSERT INTO users (name, email, age)
VALUES ('张三', 'zhangsan@example.com', 26)
ON DUPLICATE KEY UPDATE age = 26, name = '张三';
-- 或者忽略重复键的插入
INSERT IGNORE INTO users (name, email, age)
VALUES ('张三', 'zhangsan@example.com', 26);

UPDATE table_name
SET column1 = value1, column2 = value2, ...
WHERE condition;

UPDATE users 
SET email = 'new_email@example.com'
WHERE id = 1;

UPDATE users 
SET 
    name = '张三丰',
    age = 28,
    email = 'zhangsanfeng@example.com'
WHERE id = 1;

-- 年龄增加1岁
UPDATE users 
SET age = age + 1
WHERE id = 1;
-- 字符串拼接
UPDATE users 
SET name = CONCAT(name, '先生')
WHERE gender = '男';

-- 将有订单的用户标记为活跃用户
UPDATE users 
SET is_active = TRUE
WHERE id IN (SELECT DISTINCT user_id FROM orders);

-- 使用 CASE 条件更新
UPDATE users 
SET age_group = 
    CASE 
        WHEN age < 20 THEN '青少年'
        WHEN age BETWEEN 20 AND 40 THEN '青年'
        ELSE '中年及以上'
    END;

DELETE FROM table_name
WHERE condition;

DELETE FROM users 
WHERE id = 1;

-- 删除所有未激活的用户
DELETE FROM users 
WHERE is_active = FALSE;
-- 删除年龄大于100的用户
DELETE FROM users 
WHERE age > 100;

-- 删除没有订单的用户
DELETE FROM users 
WHERE id NOT IN (SELECT DISTINCT user_id FROM orders);

-- 删除所有记录
DELETE FROM users;
-- 更快的清空表方式（不可回滚）
TRUNCATE TABLE users;

SELECT column1, column2, ...
FROM table_name
[WHERE condition]
[ORDER BY column1 [ASC|DESC], column2 [ASC|DESC], ...]
[GROUP BY column1, column2, ...]
[HAVING condition]
[LIMIT number];

SELECT * FROM users;

SELECT name, email FROM users;

    SELECT 
    name AS 姓名, 
    email AS 邮箱,
    age AS 年龄
FROM users;

-- 简单条件
SELECT * FROM users WHERE age > 25;
-- 多条件组合
SELECT * FROM users 
WHERE age > 25 AND name LIKE '张%';
-- 使用 IN
SELECT * FROM users 
WHERE age IN (25, 30, 35);
-- 使用 BETWEEN
SELECT * FROM users 
WHERE age BETWEEN 25 AND 35;
-- 使用 IS NULL
SELECT * FROM users 
WHERE email IS NULL;

-- 单字段排序
SELECT * FROM users ORDER BY age DESC;
-- 多字段排序
SELECT * FROM users 
ORDER BY age DESC, name ASC;

-- 前10条记录
SELECT * FROM users LIMIT 10;
-- 分页查询：从第20条开始，取10条
SELECT * FROM users LIMIT 20, 10;
-- 或者使用新语法
SELECT * FROM users LIMIT 10 OFFSET 20;

-- 获取所有不同的年龄
SELECT DISTINCT age FROM users;

-- 计数
SELECT COUNT(*) FROM users;
SELECT COUNT(DISTINCT age) FROM users;
-- 求和、平均、最大、最小
SELECT 
    COUNT(*) AS 总人数,
    AVG(age) AS 平均年龄,
    MAX(age) AS 最大年龄,
    MIN(age) AS 最小年龄,
    SUM(age) AS 年龄总和
FROM users;

-- 按年龄分组统计
SELECT 
    age,
    COUNT(*) AS 人数
FROM users
GROUP BY age;
-- 分组后筛选
SELECT 
    age,
    COUNT(*) AS 人数
FROM users
GROUP BY age
HAVING COUNT(*) > 5;

-- 内连接
SELECT 
    u.name,
    o.order_id,
    o.order_date
FROM users u
INNER JOIN orders o ON u.id = o.user_id;
-- 左连接
SELECT 
    u.name,
    o.order_id
FROM users u
LEFT JOIN orders o ON u.id = o.user_id;
-- 多表连接
SELECT 
    u.name,
    p.product_name,
    oi.quantity
FROM users u
JOIN orders o ON u.id = o.user_id
JOIN order_items oi ON o.order_id = oi.order_id
JOIN products p ON oi.product_id = p.id;

-- 在 WHERE 中使用子查询
SELECT * FROM users 
WHERE age > (SELECT AVG(age) FROM users);
-- 在 FROM 中使用子查询（派生表）
SELECT *
FROM (
    SELECT name, age FROM users WHERE age > 25
) AS adult_users;
-- 在 SELECT 中使用子查询
SELECT 
    name,
    age,
    (SELECT COUNT(*) FROM orders WHERE user_id = users.id) AS order_count
FROM users;