Joins (1/48)
What is a JOIN in MySQL, and why is it used?
    Understanding JOINs in MySQL

    A JOIN in MySQL is used to combine rows from two or more tables based on a related column between them. JOINs allow you to query data that is logically connected but stored across multiple tables for normalization, consistency, and performance.

    1. Why JOINs Are Used
    • • To retrieve related data stored in multiple tables.
    • • To avoid data duplication by using normalized table structures.
    • • To perform complex queries that require data relationships.
    • • To improve data integrity and maintain clean database design.
    2. Types of JOINs in MySQL
    • **a. INNER JOIN**
    • • Returns only matching rows between tables.
    • • Most commonly used join.
    • **Example:**
    • ```sql
    • SELECT users.id, users.name, orders.amount
    • FROM users
    • INNER JOIN orders ON users.id = orders.user_id;
    • ```
    • **b. LEFT JOIN (LEFT OUTER JOIN)**
    • • Returns all rows from the left table and matching rows from the right table.
    • • Non-matching rows from the right table appear as NULL.
    • **c. RIGHT JOIN (RIGHT OUTER JOIN)**
    • • Opposite of LEFT JOIN — returns all rows from the right table.
    • **d. FULL OUTER JOIN**
    • • MySQL does not support this directly.
    • • Can be simulated using UNION between LEFT and RIGHT JOIN.
    • **e. CROSS JOIN**
    • • Produces a Cartesian product (all combinations).
    • • Usually used for generating data sets.
    3. When to Use JOINs
    • • To fetch user details along with their orders.
    • • To connect posts with authors, comments, tags, etc.
    • • To aggregate data across multiple related tables.
    • • To enforce normalized relational schema while still retrieving combined data.

    JOINs are fundamental for working with relational databases because they allow efficient, structured, and meaningful data retrieval across multiple tables.