by Markus Winand.
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.
Book-Section: Index-Organized Tables
Glossary: Heap-Table — Tables stored in an unordered fashion.
Glossary: Clustered Index — Table stored in a B-Tree index
Glossary: Index-Organized Table — Oracle clustered index
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Markus Winand provides insights into SQL and shows how different systems support it at modern-sql.com. Previously he made use-the-index-luke.com, which is still actively maintained. Markus can be hired as trainer, speaker and consultant via winand.at.
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