数据表多对多
今天学习了数据表多对多,由于有图理解起来也轻松了很多,
使用联合主键进行多对多表的关系的管理(中间表)
create database auth character set UTF8; /*用户表*/ create table users( id varchar(32) primary key, name varchar(30), pwd varchar(32) ); /*创建角色表*/ create table roles( id varchar(32) primary key, name varchar(30), des varchar(100) ); /*通过一个中间表映射多对多的关系,多对多就是多个一对多 联合主键的特点是:两个列不能同时重复 */ create table roleuser( uid varchar(32), rid varchar(32), constraint ru_pk primary key(uid,rid), constraint ru_fk1 foreign key(uid) references users(id), constraint ru_fk2 foreign key(rid) references roles(id) ); /*创建菜单表*/ create table menus( id varchar(32) primary key, name varchar(50), url varchar(100) ); /*关联角色到菜单*/ create table rolemenu( mid varchar(32), rid varchar(32), constraint rm_pk primary key(mid,rid), constraint rm_fk1 foreign key(mid) references menus(id), constraint rm_fk2 foreign key(rid) references roles(id) )
E-R图 (Entry-Relationship 实体关系图)
写入表中几行数据进行基本分析
insert into users values('U001','Jack','1234'); insert into users values('U002','张三','4321'); insert into users values('U003','Tom','1111'); insert into roles values('R001','管理员',''); insert into roles values('R002','教师',''); insert into roleuser values('U001','R001'); insert into roleuser values('U002','R002'); insert into menus values('M001','系统管理','/sys.jsp'); insert into menus values('M002','用户管理','/user.jsp'); insert into menus values('M003','角色管理','/role.jsp'); insert into rolemenu values('M001','R001'); insert into rolemenu values('M002','R001'); insert into rolemenu values('M003','R001'); insert into rolemenu values('M003','R002');
进行查询
/*查询某个人拥有某个角色*/ select u.name,r.name from users u inner join roleuser ru on u.id=ru.uid inner join roles r on ru.rid=r.id; /*某角色拥有某菜单*/ select r.name,m.name from roles r inner join rolemenu rm on r.id=rm.rid inner join menus m on rm.mid=m.id; /*查询某人拥有某个菜单*/ select m.* from users u inner join roleuser ru on u.id=ru.uid inner join roles r on ru.rid=r.id inner join rolemenu rm on r.id=rm.rid inner join menus m on rm.mid=m.id;