mysql如何写sql语句

-- 创建数据库
CREATE DATABASE my_database;

-- 使用数据库
USE my_database;

-- 创建表
CREATE TABLE users (
    id INT AUTO_INCREMENT PRIMARY KEY,
    username VARCHAR(50) NOT NULL,
    email VARCHAR(100) NOT NULL UNIQUE,
    created_at TIMESTAMP DEFAULT CURRENT_TIMESTAMP
);

-- 插入单条记录
INSERT INTO users (username, email) VALUES ('john_doe', 'john@example.com');

-- 插入多条记录
INSERT INTO users (username, email) VALUES 
('jane_doe', 'jane@example.com'),
('jim_smith', 'jim@example.com');

-- 选择所有列
SELECT * FROM users;

-- 选择特定列
SELECT username, email FROM users;

-- 带条件查询
SELECT * FROM users WHERE id = 1;

-- 排序查询结果
SELECT * FROM users ORDER BY created_at DESC;

-- 分组查询
SELECT username, COUNT(*) as user_count FROM users GROUP BY username;

-- 更新记录
UPDATE users SET email = 'new_email@example.com' WHERE id = 1;

-- 删除记录
DELETE FROM users WHERE id = 1;

-- 删除表
DROP TABLE users;

-- 删除数据库
DROP DATABASE my_database;