Secondary Index

A secondary index is an index that refers to a clustered index (SQL Server, MySQL/InnoDB) or Index-Organized Table (Oracle). In other words, an index on an index.

Accessing table data via a secondary index is slower than a similar query on a heap-table.

About the Author

Photo of Markus Winand
Markus Winand tunes developers for high SQL performance. He also published the book SQL Performance Explained and offers in-house training as well as remote coaching at