Here’s a clean and structured explanation of LEFT JOIN and RIGHT JOIN using tables in a readable way:
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.
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 |
Table: Departments
DepartmentID | DepartmentName |
---|---|
101 | HR |
102 | IT |
103 | Finance |
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.
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.
Key Differences
Feature | LEFT JOIN | RIGHT JOIN | ||||||||||||
---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|
|
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. |
- 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.
By presenting tables neatly and explaining key concepts with examples, the structure remains easy to understand and visually appealing.
The above is the detailed content of Mastering SQL Joins: LEFT JOIN vs RIGHT JOIN Explained with Examples. For more information, please follow other related articles on the PHP Chinese website!

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