Understanding MySQL LEFT JOIN

What is LEFT JOIN?

LEFT JOIN, also known as LEFT OUTER JOIN, combines rows from two tables based on a related column between them.

It returns all rows from the left table and the matched rows from the right table. If no match exists, the result includes NULLs for the right table columns.

• Includes all rows from the left table.
• Matches rows from the right table where possible.
• Fills unmatched right table columns with NULL.

Syntax of LEFT JOIN

The basic syntax for a LEFT JOIN in MySQL is straightforward and easy to use.

• SELECT columns FROM left_table
• LEFT JOIN right_table ON left_table.common_column = right_table.common_column;

Example of LEFT JOIN

Consider two tables: Customers and Orders. We want to list all customers and their orders, including customers with no orders.

When to Use LEFT JOIN

LEFT JOIN is ideal when you need to preserve all records from the left table, regardless of matching records in the right table.

• Retrieve all customers and their orders, including customers without orders.
• Find unmatched records in one table compared to another.
• Generate reports that require complete data from one table.