[英]Double Foreign key in postgresql
I am trying to use a double primary key as a foreign key. 我试图使用双主键作为外键。
Create table AAA (
AAA_id int primary key
);
create table BBB (
AAA_id int,
BBB_name character varying(20),
primary key (AAA_id, BBB_name)
);
create table CCC (
AAA_id,
BBB_name,
DDD_id,
... ???
);
table AAA is an object 表AAA是一个对象
table BBB is many to one with AAA, and holds aliases of AAA 表BBB与AAA有多对一,并且拥有AAA的别名
I am trying to create a pivot table, CCC which holds a many to one between DDD and BBB. 我正在尝试创建一个数据透视表,CCC在DDD和BBB之间保持多对一。
I guess I want something like 我想我想要的东西
create table CCC (
AAA_id,
BBB_name,
DDD_id,
foreign key (AAA_id, BBB_name) references BBB(AAA_id, BBB_name) on update cascade
);
where both AAA_id and BBB_name are foreign keys, but they are also always referring to the same row in BBB. 其中AAA_id和BBB_name都是外键,但它们也始终引用BBB中的同一行。
but of course that's not valid. 但当然这是无效的。 what is the best way to produce this type of behavior in postgreSQL? 在postgreSQL中产生这种行为的最佳方法是什么?
Create temp table AAA (
AAA_id int primary key
);
create temp table BBB (
AAA_id int not null references AAA (AAA_id),
BBB_name character varying(20) not null,
primary key (AAA_id, BBB_name)
);
create temp table CCC (
AAA_id int not null,
BBB_name character varying(20) not null,
DDD_id integer not null,
-- Guessing at the primary key.
primary key (AAA_id, BBB_name, DDD_id),
foreign key (AAA_id, BBB_name) references BBB (AAA_id, BBB_name)
on update cascade
);
Since {AAA_id, BBB_name} uniquely identify a row in BBB, the foreign key {AAA_id, BBB_name} in CCC will also reference one unique row in BBB. 由于{AAA_id,BBB_name}唯一地标识BBB中的行,因此CCC中的外键{AAA_id,BBB_name}也将引用BBB中的一个唯一行。
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