AI engineering glossary · SQL databases
What is covering index?
Covering index (also called Index-only scan): An index that contains every column a query needs, so the database answers it from the index alone without visiting the table. It avoids extra reads but makes the index larger.
Covering index: an example
With an index on (customer_id, amount), SELECT SUM(amount) WHERE customer_id = 5 reads only the index.
Related terms
More SQL databases terms
Where you learn it
Covering index is part of the AI Engineering Program, which teaches it with notes, a hands-on lab and an exam. The first lesson is free.