Why Isn't My Query Using an Index? Databases for Developers: Performance #5

You've created your index. All it's columns appear in your query's where clause. There are no functions on them. But the database has still decided to go for a full table scan!

Why?!

This video explores some of the reasons why using an index may be slower than a full table scan. Including one of the most important reason: the clustering factor.

Need help with SQL?

Ask us over on AskTOM: https://asktom.oracle.com

Twitter: https://twitter.com/ChrisRSaxon
Daily SQL Twitter tips: https://twitter.com/SQLDaily
All Things SQL blog: https://blogs.oracle.com/sql/
Test your SQL Skills on the Oracle Dev Gym: https://devgym.oracle.com/

============================
The Magic of SQL with Chris Saxon

Copyright © 2020 Oracle and/or its affiliates. Oracle is a registered trademark of Oracle and/or its affiliates. All rights reserved. Other names may be registered trademarks of their respective owners. Oracle disclaims any warranties or representations as to the accuracy or completeness of this recording, demonstration, and/or written materials (the “Materials”). The Materials are provided “as is” without any warranty of any kind, either express or implied, including without limitation warranties or merchantability, fitness for a particular purpose, and non-infringement.

Видео Why Isn't My Query Using an Index? Databases for Developers: Performance #5 канала The Magic of SQL