In MySQL, the JOIN operation is used to combine rows from two or more tables based on a related column between them. It allows you to retrieve data from multiple tables in a single query, creating a meaningful and complete dataset. There are several types of JOIN in MySQL, each serving a specific purpose. Here are the most common types of JOIN with real-time examples and explanations:

1. INNER JOIN:

An INNER JOIN retrieves only the rows that have matching values in both tables being joined. It returns rows where there is a match in the specified column(s) between the tables.

Example:

Suppose you have two tables, orders and customers, with the following columns:

• orders: order_id, customer_id, order_date, order_total
• customers: customer_id, customer_name

You want to retrieve a list of orders along with the corresponding customer names.

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SELECT orders.order_id, customers.customer_name
FROM orders
INNER JOIN customers ON orders.customer_id = customers.customer_id;

• In this example, we use an INNER JOIN to combine the orders and customers tables based on the customer_id column.
• The result set includes only rows where there is a matching customer_id in both tables.
• This query retrieves a list of order IDs along with the corresponding customer names.

2. LEFT JOIN (or LEFT OUTER JOIN):

A LEFT JOIN retrieves all rows from the left table and the matched rows from the right table. If there is no match in the right table, the result will contain NULL values for columns from the right table.

Example:

Suppose you have two tables, employees and departments, with the following columns:

• employees: employee_id, employee_name, department_id
• departments: department_id, department_name

You want to retrieve a list of all employees and their corresponding department names, including employees who are not assigned to any department.

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SELECT employees.employee_name, departments.department_name
FROM employees
LEFT JOIN departments ON employees.department_id = departments.department_id;