RIGHT JOIN

Introduction

RIGHT JOIN is the mirror of LEFT JOIN — it keeps all rows from the right table. In practice, almost everyone writes LEFT JOIN with the tables flipped, but you'll see RIGHT JOIN occasionally.

Understanding the topic

Core concepts to understand:

• FROM a RIGHT JOIN b ON ....
• All B rows kept; A columns NULL when no match.
• Stylistic preference: most teams use only LEFT JOIN.
• Useful when the natural reading order keeps the 'main' table on the right.
• Same performance as LEFT JOIN.

Syntax reference

Visual workflow / architecture:

RIGHT JOIN  orders  ──▶  users
 every order kept; user side may be NULL if data is bad

SELECT <cols>
FROM   <a> [AS a]
RIGHT JOIN <b> [AS b]
       ON  <a.key> = <b.key>;

SELECT u.name, o.amount
FROM   users  u
RIGHT JOIN orders o ON o.user_id = u.id;

Real-world use

Audit queries like 'every order, even if its user record is missing/deleted' sometimes read more naturally as RIGHT JOIN.

Best practices

• Stick to LEFT JOIN for consistency unless RIGHT reads more naturally.
• Same indexing rules as LEFT JOIN.
• Code reviews often suggest flipping RIGHT to LEFT.

Hands-on exercise

Interview preparation — practice these questions:

• Q1. RIGHT vs LEFT JOIN.
• Q2. Why is RIGHT JOIN uncommon?
• Q3. Convert a RIGHT JOIN to a LEFT JOIN.
• Q4. Performance differences.
• Q5. Use case where RIGHT is clearer.