Natural Join in SQL

In this article, we will explore “Natural Join in SQL” with examples. Let’s get started.

What is Natural Join in SQL ?

A NATURAL JOIN in SQL automatically joins two tables based on columns with the same name and data type in both tables. It doesn’t require specifying the join condition explicitly. It’s essential to have columns with the same name and data type in both tables for a successful natural join.

Example: Natural Join in SQL

Here’s an example of a NATURAL JOIN between two tables where the columns have the same name. In this example, we have two tables, Employees and Departments, with the same column name, DepartmentID:

Employees Table:

EmployeeID	EmployeeName	DepartmentID	Salary
1	John	101	5000
2	Emily	102	5500
3	Michael	103	6000
4	Sarah	101	4800
5	David	104	5200

Departments Table:

DepartmentID	DepartmentName
101	HR
102	IT
103	Sales
104	Marketing

Now, let’s use a NATURAL JOIN to retrieve a list of employees along with their respective department names:

SELECT EmployeeName, DepartmentName, Salary
FROM Employees
NATURAL JOIN Departments;

Result of the NATURAL JOIN:

EmployeeName	DepartmentName	Salary
John	HR	5000
Emily	IT	5500
Michael	Sales	6000
Sarah	HR	4800
David	Marketing	5200

In this example, the NATURAL JOIN automatically joins rows where the DepartmentID column has the same name in both tables, resulting in a list of employees with their respective department names and salaries.

Advantages of Natural Join

1. Simplicity: Natural Joins simplify queries by matching rows based on columns with the same names, reducing the need for explicit join conditions.
2. Maintenance Ease: They adapt to changes in column names, requiring less query maintenance.
3. Efficiency: Natural Joins can be efficient, especially for large datasets, as the database engine optimizes the operation.

Disadvantages of Natural Join

1. Ambiguity: Natural Joins can lead to ambiguity in queries when multiple columns share the same name.
2. Limited Control: They offer limited control over join conditions, which can be a drawback in complex scenarios.
3. Unintended Joins: Changes in column names or the addition of similar-named tables can lead to unintended joins, causing incorrect results.
4. Performance Variability: Natural Joins may not always result in the most optimal query execution plan.
5. Compatibility: Not all database systems support Natural Joins, and behavior may vary between vendors, impacting portability.

Database Systems that support NATURAL JOIN in SQL

The below databases support Natural Join in SQL.

1. MySQL
2. PostgreSQL
3. Oracle Database
4. SQLite
5. IBM Db2
6. MariaDB

Natural Join vs Inner Join

Aspect	NATURAL JOIN	INNER JOIN
Definition	Automatically joins tables based on columns with the same name.	Requires specifying join conditions explicitly.
Control	Offers limited control over join conditions, as it relies on matching column names.	Provides full control over join conditions, allowing custom and complex conditions.
Ambiguity Risk	May result in ambiguity if tables have multiple columns with the same name.	Reduces the risk of ambiguity by explicitly specifying join conditions.
Column Naming Convention	Requires consistent column naming conventions for automatic matching.	Offers flexibility in naming columns but requires explicit join conditions.
Query Example	SELECT * FROM Employees NATURAL JOIN Departments;	SELECT Orders.OrderID, Customers.CustomerName, Orders.OrderDate FROM Orders INNER JOIN Customers ON Orders.CustomerID = Customers.CustomerID;
Use Case Example	Retrieving data from related tables with matching column names.	Joining tables based on specific criteria or when column names differ.
Portability	Compatibility can vary between database systems. Not universally supported.	Universally supported across database systems.
Performance Consideration	May have performance implications for large datasets due to automatic matching.	Offers more control over performance optimization through explicit join conditions and indexing.

Conclusion : Natural Join in SQL

In this article, we explored the concept of a NATURAL JOIN in SQL, which automatically combines tables based on matching column names and data types. We provided an example of a NATURAL JOIN between two tables and discussed its advantages, such as simplicity and maintenance ease, as well as its disadvantages, including potential ambiguity and limited control.

We also listed databases that support NATURAL JOIN and compared it to the more versatile INNER JOIN in a tabular format, highlighting the differences between the two join types.

Finally, we concluded that the choice between NATURAL JOIN and INNER JOIN depends on specific query requirements and database considerations, with INNER JOIN being the preferred choice in most scenarios due to its greater control and compatibility.

Related Articles :

Inner Join in SQL

Cross Join in SQL: Comprehensive Guide