mysql 去除多余项

-- 创建示例表
CREATE TABLE users (
    id INT AUTO_INCREMENT PRIMARY KEY,
    name VARCHAR(100),
    email VARCHAR(100) UNIQUE
);

-- 插入重复数据
INSERT INTO users (name, email) VALUES ('Alice', 'alice@example.com');
INSERT INTO users (name, email) VALUES ('Bob', 'bob@example.com');
INSERT INTO users (name, email) VALUES ('Alice', 'alice@example.com');

-- 查询重复数据
SELECT email, COUNT(*)
FROM users
GROUP BY email
HAVING COUNT(*) > 1;

-- 删除重复数据
DELETE u1 FROM users u1
JOIN users u2 
WHERE u1.id > u2.id AND u1.email = u2.email;

-- 创建示例表
CREATE TABLE logs (
    id INT AUTO_INCREMENT PRIMARY KEY,
    message TEXT,
    created_at TIMESTAMP DEFAULT CURRENT_TIMESTAMP
);

-- 插入示例数据
INSERT INTO logs (message) VALUES ('Log message 1');
INSERT INTO logs (message) VALUES ('Log message 2');

-- 删除一个月前的日志数据
DELETE FROM logs
WHERE created_at < NOW() - INTERVAL 1 MONTH;