RIGHT JOIN in MySQL - Practice Problems & Coding Challenges

Challenge - 5 Problems

❓ query_result

intermediate

What is the output of this RIGHT JOIN query?

Given two tables, Employees and Departments, what will be the result of the following query?

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

MySQL

CREATE TABLE Employees (ID INT, Name VARCHAR(20), DepartmentID INT);
INSERT INTO Employees VALUES (1, 'Alice', 10), (2, 'Bob', 20), (3, 'Charlie', NULL);
CREATE TABLE Departments (ID INT, DepartmentName VARCHAR(20));
INSERT INTO Departments VALUES (10, 'HR'), (20, 'Engineering'), (30, 'Marketing');

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

A [('Alice', 'HR'), ('Bob', 'Engineering'), (NULL, 'Marketing')]

B [('Alice', 'HR'), ('Bob', 'Engineering')]

C [('Alice', 'HR'), ('Bob', 'Engineering'), ('Charlie', NULL), (NULL, 'Marketing')]

D [('Charlie', NULL), (NULL, 'Marketing')]

💡 Hint

Remember, RIGHT JOIN returns all rows from the right table, and matching rows from the left table.

The RIGHT JOIN returns all departments, even if no employee belongs to them. 'Marketing' has no employee, so employee name is NULL. 'Charlie' has no department, so he is excluded.

🧠 Conceptual

intermediate

Which statement best describes RIGHT JOIN?

Choose the correct description of what a RIGHT JOIN does in SQL.

A Returns all rows from the left table and matching rows from the right table.

B Returns all rows from both tables, combining them fully.

C Returns all rows from the right table and matching rows from the left table.

D Returns only rows that have matching values in both tables.

💡 Hint

Think about which table's rows are always included in the result.

RIGHT JOIN returns all rows from the right table, and matching rows from the left table. If no match, left table columns are NULL.

📝 Syntax

advanced

Identify the syntax error in this RIGHT JOIN query

Which option contains a syntax error in the RIGHT JOIN usage?

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

A SELECT e.Name, d.DepartmentName FROM Employees e RIGHT JOIN Departments d WHERE e.DepartmentID = d.ID;

B ;DI.d = DItnemtrapeD.e NO d stnemtrapeD NIOJ THGIR e seeyolpmE MORF emaNtnemtrapeD.d ,emaN.e TCELES

C ELECT e.Name, d.DepartmentName FROM Employees e RIGHT JOIN Departments d ON e.DepartmentID = d.ID;

D SELECT e.Name, d.DepartmentName FROM Employees e RIGHT JOIN Departments d ON e.DepartmentID = d.ID;

💡 Hint

Check the placement of the ON clause in JOIN syntax.

The ON clause must follow the JOIN keyword directly. Using WHERE instead causes a syntax error.

❓ optimization

advanced

How to optimize a RIGHT JOIN query for better performance?

You have a RIGHT JOIN query joining large tables. Which option is the best way to optimize it?

A Replace RIGHT JOIN with LEFT JOIN and swap table order.

B Add indexes on the join columns in both tables.

C Use SELECT * to fetch all columns for faster retrieval.

D Remove the ON clause to reduce complexity.

💡 Hint

Think about how databases speed up join operations.

Indexes on join columns help the database find matching rows faster, improving join performance.

🔧 Debug

expert

Why does this RIGHT JOIN query return fewer rows than expected?

Given these tables:

Employees: ID, Name, DepartmentID
Departments: ID, DepartmentName

Query:

SELECT e.Name, d.DepartmentName
FROM Employees e
RIGHT JOIN Departments d ON e.DepartmentID = d.ID
WHERE e.Name IS NOT NULL;

Why might this query return fewer rows than a RIGHT JOIN without the WHERE clause?

A The query syntax is invalid and causes an error.

B RIGHT JOIN ignores the WHERE clause, so it returns all rows anyway.

C The ON condition is incorrect, causing fewer matches.

D The WHERE clause filters out rows where e.Name is NULL, removing unmatched right table rows.

💡 Hint

Consider how WHERE filters rows after the join.

The WHERE clause removes rows where e.Name is NULL, which are the unmatched rows from the right table. This reduces the result set.