Respuesta :
Answer:
Foreign key is a part of the DBMS. It stands for a database management system.
Foreign key use can be given as:
It is key that used to link two tables together.
It used as a reference to the primary key.
To define any foreign key we references keyword.
Example:
A)
create table product
(
P_id number(4) primary key,
P_name varchar2(30),
);
insert into product(P_id ,P_name )values(1001,'X');
insert into product(P_id ,P_name)values(1003,'y');
insert into product(P_id ,P_name)values(1005,'z');
B)
create table productdetail
(
pd_id number(4) references P_id number(4) ,
pd_city varchar2(50),
pd_price number(5)
);
insert into productdetail(pd_id ,pd_city, pd_price)values(1001,'kanpur',2100);
insert into productdetail(pd_id ,pd_city, pd_price)values(1003,'delhi',1200);
insert into productdetail(pd_id ,pd_city, pd_price)values(1005,'agra',205);
C)
query for related data :
select * from product,productdetail where product.P_id=productdetail.pd_id;
Explanation:
In point A we declare a table i.e product. In this table, we create two-column P_id which is a primary key, P_name.
In point B we create a table i.e productdetail. In this table, we create three column pd_id which is a foreign key that works as a reference for the primary key,pd_city,pd_price.
In point C. It gives the data from both the table.
