Why Do Relational Databases Use Primary Keys and Foreign Keys?

Why Do Relational Databases Use Primary Keys and Foreign Keys?

The name says relational database. The database relationships can be defined with respect to key columns. These key columns can be identified based on cardinality. This is the reason why Relational Databases Use Primary Keys and Foreign Keys.

Let us take an example of the Customer and Location. So any transaction that happened, we usually say customer A purchased Product X from Location Z, and these relationships can be specified using SQL Joins.

Because it has Primary Key and Foreign Key Relationships.

Using the above statement one can say that there is a relationship between customer, product, and location.

Use Of Primary Keys and Foreign Keys?

In DBMS primary key and foreign key are very identical and therefore there are a lot of interview questions we usually encounter on the basic concepts of the primary key. Also on how it is related to a foreign key.

To start with a primary key. It is a candidate key with no null values. A candidate key is any key with the help of which we are able to uniquely identify a record of a table.

That means we are able to uniquely identify a record of the table with the help of a candidate key and that candidate key should not have any null values in it.

This means the records of that particular candidate key should not be void or empty.

let’s take an example of table1 that is department. Let the department table have three attributes.

The attributes are department ID, department name, and the address of the department.

Let me fill in the values of the table that the department ID is d1, d2,d3, and d4, and so on.

Let the department name be some XYZ, ABC, QPR, and XYZA that they dress be some random address values because we do not refer it in this example.

Now for this particular table department, let us say the department ID is the primary key. Now if Department ID is the primary key.

Each record in the department ID attribute should be unique and there should be no null values in this department ID. Which holds in this particular case.

A foreign key is identical to the primary key since the foreign key is basically a reference of the primary key into some other table.

First, let us take an example, and then we’ll go to the definition of what a foreign key is.

 Let us consider another table the table name as an employee.

Now let us define the attributes of the table as employee ID, employee name, address of the employee, and the department to which the employee belongs, that is department ID.

Relational Database Primary Key and Foreign Key Dependency

Consider table one again the department table had three attributes mentioning department ID, department name, and address of the department.

The employee table has four attributes referring to employ ID, the name of the employee the address where the employee stays, and the department in which the employee works.

Let me fill in some random values in this table. Let the address be some random values again.

Just to understand the concept of primary key and foreign key let us fill any random data into it.

These two tables have interdependency based on key columns.

Again, let us say that employee E1 works in department D1. Employee E2 to also works in department D1 employee E3 works in departments D 3 and D4 for each work in the department.

The department ID in the department table is the primary key and the same department ID in the employee table can denote as a foreign key.

Also, the rule is that the foreign key of any table should be the primary key in the reference table.

This is the concept of primary key and parent key to knowing the differences between primary key and foreign key.

Features of Primary Keys and Foreign keys

  • To create physical relationships
  • To create Logical Relationships
  • Create Databases

To Create Physical Relationships

Physical database design translates the logical data model into a group of SQL statements that outline the database. For electronic database systems, it’s relatively easy to translate from a logical data model into a physical data model.

To Create Logical Relationships

A logical relationship may be a path between two segments that are related logically and not physically. It’s possible to possess a relationship between the segments of 1 particular database.

Create Databases

Database handlers create a database in such how that just one set of software programs provides access to data to all or any of the users.

The main purpose of the database is to work an outsized amount of data by storing, retrieving, and managing data within the database.

There are many dynamic websites worldwide. These are handled through databases. for instance, a model that checks the supply of rooms during a hotel.

We can say that this is an example of a dynamic website that uses a database.

There are many databases out there like MySQL, Oracle, MongoDB, Sybase, Informix, PostgreSQL, SQL Server, etc.

SQL or Structured command language is employed to work on the info stored during a database. SQL mainly depends on relational algebra concepts and tuple relational calculus.


A relational database management system consists of logically related tables, joins, coordinates and it has interdependency on each other that is why Relational Databases Use Primary Keys and Foreign Keys.

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