In the real world, we have to use
constraints that are not only dependent upon one table rather on two tables.
This kind of setup is known as Primary Key - Foreign key constraint or also
known as “Referential Integrity”. For e.g. lets see the example below:
a.
Dept Table
b.
Emp Table
In order to determine the relationship,
we have taken a column “Deptno” in Emp table which is validated from “Dept” table. It means “Emp” table’s column
Deptno is having all the values from the Dept table and it cannot have a value that
is not there in the Dept Table.
To define the foreign key constraint,
we can use the following syntax:
FOREIGN KEY / REFRENTIAL INTEGRITY
Create Table
EmpTemp1
(
deptno numeric(10) constraint fk references dept(deptno)
)
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