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表操作 ​

创建 ​

sql
CREATE TABLE users (
  id INT AUTO_INCREMENT PRIMARY KEY,
  username VARCHAR(50) NOT NULL,
  password VARCHAR(100) NOT NULL,
  created_time TIMESTAMP DEFAULT CURRENT_TIMESTAMP
);
sql
-- 将 orders 表中所有的数据复制到新创建的表
CREATE TABLE orders_archived
AS
SELECT * FROM orders;

约束 ​

sql
-- 为 username 增加唯一性约束
ALTER TABLE users ADD UNIQUE (username);
-- 如果重复插入返回下面错误
-- ERROR 1062 (23000): Duplicate entry 'limy' for key 'users.username'

插入数据 ​

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

# 示例
INSERT INTO users (username, password) VALUES ('limy', '123456');

增加新字段 ​

语法：ALTER TABLE table_name ADD COLUMN new_column_name data_type constraints;

sql
ALTER TABLE customers ADD COLUMN delete_at Date NULL DEFAULT NULL