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9 January 2023

Difference Between Primary key and Foreign key in DBMS

The fundamental difference is the primary key is used to guarantee that each column's value is unique but the foreign key is what links the two tables together. Let us discuss some more differences between Primary Key and Foreign Key in DBMS with the help of the comparison given below.

What is the primary key?

A main key often emphasizes the table's uniqueness. It is a column or group of columns that differentiates each row in the database in a special way. It should not contain any duplicate values, according to this. Additionally, it doesn't have a NULL value. There must be just one primary key for every database.

What is a foreign key?

Typically, a foreign key is utilized to establish a connection between the two tables. To maintain data integrity between two different instances of an object, the foreign key's primary function is to be used.

Difference between primary key and foreign key:

  • In a relational database management system, a primary key constraint is a column or set of columns that uniquely identifies each entry in a table. A column known as a foreign key establishes a connection between two tables.
  • The primary key helps you to uniquely identify a record in the table. While a foreign key is a field in the table that is a primary key of another table. 
  • The primary key never accepts null values. While the foreign key may accept multiple null values.
  • Data in the DBMS table are physically arranged in the order of the clustered index's primary key, which is a clustered index. A clustered or non-clustered index cannot be automatically created by a foreign key.
  • A table may have just one main key. You can have multiple foreign keys on a table.
  • The value of the primary key can't be removed from the parent table. The value of foreign key value can be removed from the child table.
  • You can define the primary key simplicity on the temporary tables. You cannot define foreign keys on the local temporary tables.
  • The primary key is a clustered index. While foreign is by default, it is not clustered index. 
  • No two rows can have any identical values for a primary key. The values in a foreign key may be duplicated.
  • There is no limitation in inserting the value into the table column. While inserting any value in the foreign key table, ensure the value is present in a column of a primary key. 
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