Profile
Settings
Refer your friends
Sign out
Introduction
The keys to MySQL are essential to establishing a relationship between two tables. They can be extremely useful for maintaining an organized database structure. The major distinction between them is that the primary key can identify every record in the table while the foreign key is for connecting two tables. In this article, we’re going to go over the basic distinctions between Foreign and Primary Keys, considering different factors. Before we can make a comparison, we will briefly discuss the keys.
What is the Primary Key?
A primary key constraint is a column or a group comprising columns, which identifies each row of the table in the management system for relational databases. It is not a duplicate, meaning that a similar value cannot appear over time within the database table. A table cannot have greater value in comparison to a single primary key. Also, you can determine the primary key at the column or table level. If you are creating the primary key as a composite, you need to specify it at the table level.
What is the Foreign Key?
One can use a foreign key to refer to another table. It’s also known as a reference key. It’s a column or a group of columns that is the primary key of an additional table. Also, it is a foreign key to the table that could be considered a primary key in another table. Generally, we use foreign keys to establish a relationship between 2 different tables. Also, the primary purpose of an foreign key is to ensure the integrity of data between 2 different examples of the same entity.
Key Differences
| Primary Key | Foreign Key |
| A primary key constraint is a column representing each row of the database of the management system for relational databases. | In contrast, a foreign key can be described as a column that establishes the relationship between two databases. |
| There is only one primary key in tables. | You can have several foreign keys within tables. |
| The primary key won’t accept null values. | Foreign keys can accept null values in various ways. |
| Primary key values cannot be eliminated from a parent table. | Foreign key values may be taken out of the parent table. |
| You must ensure it is inserted in a column belonging to a primary key. | There are no limitations to inserting values in the table column when inserting any value into your foreign key tables. |
| There aren’t any two rows that can contain the same value in a primary key. | On the contrary, foreign keys can have duplicate values. |
The Difference Between the Primary Key and Foreign Key
Number of Related Tables
Primary keys are linked to one table, whereas foreign keys are linked to two tables. This is a result of the fundamental concept that there is a differentiator between the primary and foreign keys.
Duplicate Values
Another difference between primary and foreign keys is that it’s impossible to duplicate primary keys, while foreign key values could contain duplicate values.
Null Values
Additionally, the primary key value is not null. However, the value of a foreign key can be null.
Usage
The primary key helps uniquely identify records of the table, while we can use a foreign key to connect two tables. This is the major distinction between primary key and foreign key.
Number of Keys
A key difference between primary and foreign keys is that there is only one primary key in the table. However, it is possible to have several foreign keys within the table.
The primary key is necessary to establish the table in a relational database. A foreign key is a name given to one of several columns of another table that refers to the primary key of a table. Some DBMSs establish constraints on foreign keys to safeguard this connection.
