mysql数据库关联查询与多列约束

关联查询

select u.username,img.url from user u inner join images img on u.username = img.username;

多列约束(留言表leaMsg)

create table leaMsg(

  uid int(11) auto_increment primary key not null comment '主键ID，唯一性',

  comment_id int(11) not null comment '文章id',

  user_id int(11) not null comment '用户id',

  unique key comment_id (comment_id, user_id)

)engine=myisam default charset=utf8;

create table leaMsg1(

  uid int(11) auto_increment primary key not null comment '主键ID，唯一性',

  comment_id int(11) not null comment '文章id',

  user_id int(11) not null comment '用户id',

  unique key comment_id (comment_id)

)engine=myisam default charset=utf8;