MySQL Composite Indexes Explained

What is a Composite Index?

A composite index in MySQL is an index that includes more than one column. It stores the values of these columns in a sorted order to speed up searches involving those columns.

Unlike single-column indexes, composite indexes allow queries to filter or sort on multiple columns efficiently.

• Indexes multiple columns together in a specific order.
• Improves performance for queries using those columns combined.
• Supports leftmost prefix matching for query optimization.

How Composite Indexes Work

MySQL stores composite indexes in a sorted structure based on the order of columns defined in the index.

When a query filters on the leftmost columns of the composite index, MySQL can quickly locate matching rows without scanning the entire table.

• The order of columns in the index matters.
• Queries using the leftmost columns benefit the most.
• Queries skipping the first column cannot fully utilize the composite index.

Creating Composite Indexes in MySQL

You can create a composite index using the CREATE INDEX statement or when creating a table.

Specify the columns in the order that matches your most common query patterns.