MySQL数据命令

创建数据库
create database db1 charset utf8;
查看数据库
show database;
show create database db1;
select database();
选择数据库
use db1;
删除数据库
drop database db1;
修改数据库
alter database db2 charset utf8;

用户表
    create table user(
    id int,
    user varcher(16) not null unique,
    pwd varcher(32) not null
    foreign key(group_id) references group(id)
    );
用户表的添加
    insert into user(user,pwd,group_id) values
    (‘冬马和纱‘,‘123‘,‘1‘),
    (‘小母猪雪菜‘,‘123‘,‘1‘),
    (‘北原春希‘,‘123‘,‘2‘),
    (‘‘,‘‘,‘‘);
    
用户组表
    create table group(
    id int primary key auto_increment,
    group_name varcher(16)
    );
多对多表
    create table class2teacher(
    id int primary key auto_increment,
    class_id int not null,
    teacher_id int,
    constraint fk_class foreign key(class_id) references class,
    constraint fk_teacher foreign key(teacher_id) references teacher,
    unique(class_id,teacher_id)
    );
    insert into class2teacher(class_id,teacher_id) values
    (‘‘,‘‘),
    (‘‘,‘‘);

连表查询
    select user.id,user.name,group_name from 
    user inner join group on user.group_id=group.id;
子查询
    select user.name from user where group_id in 
    (select id from group where group_name=‘败犬组‘);