Covering Index

A covering index is a database optimization technique where an index includes all the columns required to satisfy a query, eliminating the need to access the underlying table data. This allows the database engine to retrieve results directly from the index, significantly improving query performance by reducing I/O operations. It is commonly used in relational databases like MySQL, PostgreSQL, and SQL Server to speed up read-heavy workloads.

Also known as: Covered Index, Index-Only Scan, Included Columns Index, Composite Index with Included Columns, Non-Key Columns Index

Why learn Covering Index?

Developers should use covering indexes when optimizing queries that frequently access specific columns, especially in read-intensive applications like reporting or analytics. They are particularly beneficial for queries with WHERE, ORDER BY, or GROUP BY clauses, as they can avoid costly table scans and reduce latency. This technique is essential for database performance tuning in high-traffic systems to ensure efficient data retrieval.

Learning Resources

• docs: MySQL Documentation: Optimizing Queries with Covering Indexes
• docs: PostgreSQL Documentation: Index-Only Scans
• tutorial: SQL Server Tutorial: Creating Covering Indexes
• video: YouTube: Covering Indexes Explained
• tutorial: Use the Index, Luke! - Covering Indexes