database:creat,drop,show,use

table:creat,delect,selsct,update

PK;constraint PK_字段 primary key(字段),

FK:constraint FK_主表_从表 foreign(外键字段) references 主表(主表主键字段)

内连接查询

select name,books from tb_login,tb_book where tb_login,user=tb_book .user;

外连接查询

左外连接

select section,tb_login.user,books,row from tb_login left join tb_book on tb_login.user=tb_book .user;

左外连接

select section,tb_login.user,books,row from tb_login left join tb_login on tb_book .user=tb_book .user;