創建表：create table users(userid,username,password,age);
插入：insert into users(username,password,age) values('ni','12','21');
（users 有四個屬性：編號、用戶名、密碼、年齡）
刪除：delete from users where userid=4;
查找：select * from users [username='xxx'];
查找：select * from table1 where field1 like ’%value1%’
修改：update users set username='rose' where userid=3;