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我正在为mysql设计一个bd-scheme。我的db存储3种点:a,b或c,路径由n对点组成:引用同一列中的外键
Route = [(a1或b1或c1; a2或b2或c2),(a2或b2或C2; A3或B3或C3),...]
create table a_points (
point_id serial not null,
owner_id bigint unsigned not null,
name varchar(20) not null,
primary key (point_id),
foreign key (owner_id) references othertable (other_id)
) engine = InnoDB;
create table b_points (
point_id serial not null,
owner_id bigint unsigned not null,
name varchar(20) not null,
fields varchar(20) not null,
primary key (point_id),
foreign key (owner_id) references othertable (owner_id)
) engine = InnoDB;
create table c_points (
point_id serial not null,
name varchar(20) not null,
cfields varchar(20) not null,
primary key (point_id)
) engine = InnoDB;
create table paths (
path_id serial not null,
name varchar(20) not null,
primary key (path_id)
) engine = InnoDB;
create table point_pairs (
pair_id serial not null,
path_id bigint unsigned not null,
point_from bigint unsigned not null,
point_to bigint unsigned not null,
table_from varchar(9) not null,
table_to varchar(9) not null,
primary key (pair_id),
foreign key (path_id) references paths (path_id)
) engine = InnoDB;
(*)的一对点的是(M,N)或从m至n
所以我存储对点连同他们的路径ID。我的问题是,我不得不创建两列来标识m和n的表名。 table_from for m和table_to for n。因此,我必须在我的代码中使用这两列来知道路径中保存了哪些点(路径和point_pairs表)。我的问题:MySql是否提供了在同一列中引用n个外键的方法?我已经考虑过加入a,b和c点表,但是我必须在这个新表中添加一个类型列,我的php类将变得毫无用处。
在此先感谢!
这是我在其他讨论中被称为“泛化专业化模式”的一个很好的总结。我将不得不了解多态协会。 – 2009-04-18 11:43:44