Part 135: Covering Indexes & Index-Only Scans

An Index-Only Scan occurs when every single column requested by a query is present directly inside the index B-Tree, completely bypassing disk access to the main table heap!

1. Creating a Covering Index with INCLUDE

CREATE INDEX idx_users_email_covering 
ON users (email) 
INCLUDE (first_name, last_name);

A query SELECT first_name, last_name FROM users WHERE email = ? resolves 100% in RAM from the index pages alone!

Key Takeaways

• Covering indexes eliminate table page fetches, multiplying query speed.

In Part 136, we explore Filtered and Partial Indexes!