// 创建数据库
CREATE DATABASE db_name;
// 删除数据库
DROP DATABASE db_name;
// 删除表
DROP TABLE table_name;

// 创建表
CREATE TABLE employee(     
    id INT NOT NULL PRIMARY KEY,     
    name VARCHAR(50),     
    city VARCHAR(50) DEFAULT "Hangzhou",     
    salary FLOAT DEFAULT "1000" 
);
// 向表中插入数据
INSERT INTO employee VALUES(1, "Tom", "Beijing", "1100");
INSERT INTO employee (id, name) VALUES(2, "Jack");
// 修改某列的默认值
ALTER TABLE employee ALTER city SET DEFAULT "Beijing";
// 删除某列的默认值
ALTER TABLE employee ALTER city DROP DEFAULT;