Explain the term foreign key and give an example (hint, for the example, provide two tables and show the relationship between them).

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.

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