Difference Between Primary key and Foreign key in DBMS
In this post, we will understand the difference between Primary key and Foreign key in DBMS
Primary key
It is used to ensure that the data in the specific column is unique.
It helps uniquely identify a record in a relational database.
One primary key only is allowed in a table.
It is a combination of the ‘UNIQUE’ and ‘Not Null’ constraints.
This means it can’t be a NULL value.
Its value can’t be deleted from parent table.
The constraint can be implicitly defined for the temporary tables.
Example- In SQL:
CREATE TABLE table_name (
col_name int NOT NULL PRIMARY KEY,
….
);
Foreign Key
It is a column or a group of columns in a relational database table.
It gives a link between the data in both the tables.
It is the field in a table which is analogous to primary key of other table.
More than one foreign key is allowed in a table.
It can contain duplicate values in a relational database.
It can contain NULL values.
Its value can be deleted from the child table.
The constraint can’t be defined on local or global temporary tables.
Example- in SQL:
CREATE TABLE table_name (
col_name int NOT NULL PRIMARY KEY,
col_name int FOREIGN KEY REFERENCES Persons(col_name)
);
Published on 25-Mar-2021 06:06:59
