What is an Index Only Scan?

Index Only Scan is an optimization in database management systems where a query can be executed using only data from the index, without accessing the main tables.

This is possible if the index contains all the columns necessary for the query (for example, in a covering index). This approach significantly speeds up query execution, as reading from the index is usually faster than from the table.

Example: if you have an index on columns id and name, and the query only selects these fields, then the DBMS can perform an Index Only Scan without loading other data from the table.