Mastering SQL Joins: LEFT JOIN vs RIGHT JOIN Explained with Examples

Here’s a clean and structured explanation of LEFT JOIN and RIGHT JOIN using tables in a readable way:

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Understanding LEFT JOIN and RIGHT JOIN in SQL

LEFT JOIN and RIGHT JOIN are types of SQL OUTER JOINs. They are used to fetch data from two tables based on a matching condition, while also including unmatched rows from one of the tables.

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1. LEFT JOIN

• The LEFT JOIN returns all rows from the left table, and the matched rows from the right table.
• If there is no match, the result contains NULL for the columns of the right table.

Syntax:

SELECT columns
FROM table1
LEFT JOIN table2
ON table1.column = table2.column;

Example:

Table: Employees

EmployeeID	Name	DepartmentID
1	Alice	101
2	Bob	102
3	Charlie	NULL
4	Diana	104

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Table: Departments

DepartmentID	DepartmentName
101	HR
102	IT
103	Finance

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Query:

SELECT Employees.Name, Departments.DepartmentName
FROM Employees
LEFT JOIN Departments
ON Employees.DepartmentID = Departments.DepartmentID;

Result:

Name	DepartmentName
Alice	HR
Bob	IT
Charlie	NULL
Diana	NULL

• All rows from Employees are included.
• Rows without a match in Departments (like Charlie and Diana) show NULL.

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2. RIGHT JOIN

• The RIGHT JOIN returns all rows from the right table, and the matched rows from the left table.
• If there is no match, the result contains NULL for the columns of the left table.

Syntax:

SELECT columns
FROM table1
RIGHT JOIN table2
ON table1.column = table2.column;

Example:

Using the same tables Employees and Departments.

Query:

SELECT Employees.Name, Departments.DepartmentName
FROM Employees
RIGHT JOIN Departments
ON Employees.DepartmentID = Departments.DepartmentID;

Result:

Name	DepartmentName
Alice	HR
Bob	IT
NULL	Finance

• All rows from Departments are included.
• Rows without a match in Employees (like Finance) show NULL.

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Key Differences

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Feature	LEFT JOIN	RIGHT JOIN
Included Rows	All rows from the left table.	All rows from the right table.
Unmatched Rows	NULL for unmatched right table.	NULL for unmatched left table.
Primary Use	Ensure all rows from the left table appear.	Ensure all rows from the right table appear.

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When to Use?

• LEFT JOIN: Use when you want all data from the left table, regardless of matches in the right table.
• RIGHT JOIN: Use when you want all data from the right table, regardless of matches in the left table.

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By presenting tables neatly and explaining key concepts with examples, the structure remains easy to understand and visually appealing.

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