---
title: "Describe the relationship between the Primary key and the Foreign key with an example in SQL."  
description: "Describe the relationship between the Primary key and the Foreign key with an example in SQL."  
author: "Revati S Misra"  
published: 2023-03-24  
updated: 2023-04-28  
canonical: https://www.mindstick.com/forum/157564/describe-the-relationship-between-the-primary-key-and-the-foreign-key-with-an-example-in-sql  
category: "mssql server"  
tags: ["database", "mssql server", "sql server", "sql"]  
reading_time: 3 minutes  

---

# Describe the relationship between the Primary key and the Foreign key with an example in SQL.

[Describe the relationship](https://www.mindstick.com/interview/33713/please-describe-the-relationship-between-seo-and-sem) between the [Primary key](https://www.mindstick.com/blog/214/primary-key) and the [Foreign key constraints](https://www.mindstick.com/blog/11170/sql-constraints) with an example in the [SQL table](https://www.mindstick.com/forum/160519/how-can-i-update-sql-table-by-dataset-data-in-ado-dot-net).

## Replies

### Reply by Aryan Kumar

In SQL, a primary key is a unique identifier for each record in a table, and a [foreign](https://yourviews.mindstick.com/story/2164/here-are-the-best-foreign-universities-for-higher-education) key is a field in one table that refers to the primary key in another table. The [relationship](https://yourviews.mindstick.com/view/80819/live-in-relationship-protecting-the-right-to-live-together) between a primary key and a foreign key is used to establish a relationship between two tables.

Let's take an example of two tables, **customers** and **orders**. The **customers** table has a primary key column called **customer_id**, and the **orders** table has a foreign key column called **customer_id** that refers to the **customer_id** column in the **customers** table.

Here's an example of how the two tables might look:

```php
-- Customers table
CREATE TABLE customers (
 customer_id INT PRIMARY KEY,
 name VARCHAR(50),
 email VARCHAR(50)
);
-- Orders table
CREATE TABLE orders (
 order_id INT PRIMARY KEY,
 customer_id INT,
 total_price DECIMAL(10,2),
 FOREIGN KEY (customer_id) REFERENCES customers(customer_id)
);
```

In this example, the **customer_id** column in the **customers** table is the primary key, and the **customer_id** column in the **orders** table is a foreign key that references the **customer_id** column in the **customers** table.

This relationship between the two tables ensures that each order is associated with a valid customer, and it helps maintain data integrity by preventing the creation of orders for non-existent customers.

Whenever a new order is added to the **orders** table, the value in the **customer_id** column must already exist in the **customers** table. This is because the foreign key constraint prevents the creation of orders for non-existent customers.

In summary, the relationship between a primary key and a foreign key in SQL is used to establish a relationship between two tables, ensuring that data is consistent and accurate.

### Reply by Krishnapriya Rajeev

The *[primary](https://www.mindstick.com/forum/33739/difference-between-primary-key-and-unique-key) key* acts as a unique identifier which helps us to identify each row in the table uniquely.

A *[foreign key](https://www.mindstick.com/blog/174/foreign-key-self-reference-constraint)* is a column found in a table which utilizes the values present in the primary key of a separate table. The values in this column can either be an already existing primary key from the referenced table or null, and cannot be anything else.

```plaintext
//Creating table 1
CREATE TABLE EMPLOYEES(emp_id int PRIMARY KEY, name varchar(20));
//Creating table 2 with a FOREIGN KEY
CREATE TABLE DEPENDANTS(dep_id int PRIMARY KEY, name varchar(20), emp_id int, FOREIGN KEY(emp_id) REFERENCES  EMPLOYEE(emp_id));
```


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Original Source: https://www.mindstick.com/forum/157564/describe-the-relationship-between-the-primary-key-and-the-foreign-key-with-an-example-in-sql

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