Primary Key vs Foreign Key: Difference and Comparison

Database management system (DBMS) is essential in business, banking, airlines, telecommunication, and universities because it is an efficient and reliable method for creating, storing, and managing database data. Relational Database Management System (RDBMS) is the advanced form of DMBS structured particularly for relational databases.

Keys are vital components of the relational database schema because they establish a link between two different tables and uniquely identify any row of data within a table. However, keys have more specific importance than just maintaining links.

It helps collect specific data from numerous rows, which would’ve been intricate or even impossible if it weren’t for keys. The two primary keys that help establish and identify links between relational databases efficiently are Primary keys and Foreign Keys.

Key Takeaways

  1. A primary key is a unique identifier for each record in a database table, ensuring that no two rows have the same primary key value.
  2. A foreign key is a field in a table that refers to the primary key of another table, establishing a relationship between the two tables and maintaining referential integrity.
  3. The main difference between primary keys and foreign keys is their function within a database, with primary keys providing a unique identifier for records. In contrast, foreign keys create relationships between tables by referencing primary keys in other tables.

Primary Key vs Foreign Key

A primary key is a choice of columns that’s unique and determines the set of rows on a particular table, and also an attribute than has an ID which is seen as a candidate key. Foreign key is a column in a table that serves as a link between two different tables, and it contains null values.

Primary Key vs Foreign Key 2

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A table cannot be a relational database table without the primary key. Because primary keys uniquely identify a specific row of data, two or more rows can’t have similar primary keys. Contrastingly, foreign keys are used to establish a relationship between the records of two different tables.


Comparison Table

Parameter of comparisonPrimary keyForeign key
Duplicate valuesPrimary keys do not permit two rows to have the same values.Foreign keys permit the two rows to have the same values.
InsertionIn primary keys, one can insert values even if the foreign key does not have that value.In foreign keys, one cannot insert values if the values are not present in the primary key.
RangeEach row in the relational database table can have only one primary key.A relational database table can have multiple foreign keys.
Clustered indexPrimary keys, by default, have a clustered index.Foreign keys do not have a clustered index.
DeletionWhen a value is to be deleted, one should make the value is still not present in the foreign keys referencing table.When a value is to be deleted, one can easily do it from foreign keys.
Temporary tablesPrimary keys can be defined on a temporary table.Foreign keys cannot be defined on a temporary table.


What is Primary Key?

A primary key refers to a particular choice of columns that uniquely determines the set of rows in a table. A primary key is a single attribute that has a unique ID and is also considered a candidate key.

The value of a primary key should never fluctuate or be changed because the primary key characterizes importance in the database. So altering the value would result in a lot of confusion.

The Primary key is cluster-indexed, meaning all the table rows are sorted. The primary key is mainly defined on a temporary table.

primary key

What is Foreign Key?

A foreign key refers to a column in a database table that provides a link between two tables. When table 1 has a primary key of table 2, this attribute is the foreign key.

Unlike primary keys, foreign keys can contain null values as it does not help identify a difference in the relation because primary keys have already done this part of the job. Foreign keys can also accept duplicate values, unlike the primary key and can have many or multiple foreign keys in a database, as foreign keys can have different attributes.

Foreign keys cannot be defined on a temporary table. While adding a value into the foreign key column, one must ensure the deal is present in the primary key and there is no constraint when deleting values from a foreign key.

foreign key

Main Differences Between Primary Key and Foreign Key

  1. Primary keys do not allow two rows in a database table to have duplicate values. Foreign keys allow two rows in a database table to have duplicate values.
  2. In the attribute of the primary keys, values can be inserted in the table even if the foreign key doesn’t have that value in its column. In the foreign keys attribute, discounts cannot be inserted in the table if the values are not in the primary key database.
  3. A primary key attribute can have only one range of primary keys in its table. A foreign key attribute can have many foreign keys in its table.
  4. Primary keys have a clustered index, meaning all the rows in the database relation are sorted. Foreign keys do not have an automatic clustered index but can be done manually.
  5. Under primary keys, a value can be deleted from the referencing table by ensuring the deal is not present in the foreign key reference table. Under foreign keys, the values can be deleted without glitches since it does not matter whether the value is still current in the primary keys reference table.
  6. Primary keys can be determined on a temporary table. Foreign keys cannot be determined or enforced on a temporary table.


Last Updated : 11 June, 2023

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10 thoughts on “Primary Key vs Foreign Key: Difference and Comparison”

  1. The comparison table is particularly useful. It provides a clear and succinct summary of the contrasting characteristics of primary keys and foreign keys.

  2. This article is lacking an in-depth explanation of primary and foreign keys. It fails to address certain advanced database query operations that involve these keys.

  3. I see the article does well in establishing that primary keys ensure uniqueness in a database table by not permitting duplicate values.

  4. The author could delve into a more extensive analysis of the specific applications of primary and foreign keys in various industry settings.

  5. I disagree. A database table can be a relational database table without the primary key. It is considered to be a bad practice, but not impossible.

  6. Avatar of Dave Williams
    Dave Williams

    The author does a poor job in understanding the role of primary keys. The fact that their values shouldn’t be changed is completely wrong. They may be updated when necessary.

  7. This article does well explaining the importance of Primary Key and Foreign Key in a DBMS. These are indispensable components of database architecture that ensure data reliability.

  8. The author does a great job in highlighting the differences between primary keys and foreign keys and their significance within a database. Very informative.

  9. I believe this article does a good job of simplifying the concept of primary and foreign keys. It makes some insightful points.

  10. Database Management Systems are the lifeblood of organizations. They help in organizing and delivering crucial data in an efficient and reliable manner.

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