10 January 2017
UKOUG Database & RAC Cloud, Infrastructure & Availability SIG Thursday 23rd February
Date: Thursday 23rd February 2017
Time: 15:30 - 16:15
“Why isn’t my query using an index?” is a common question people have when tuning SQL.
This talk explores the factors that influence the optimizer’s decision behind this question. It does so by comparing fetching rows from a database table to finding all the red M&Ms from their bags. It contrasts using an index range scan and a full table scan to do this.
It introduces the concepts of blocks and the clustering factor. It discusses how these affect the optimizer's calculations. It goes on to demonstrate how these concepts work in practice using real SQL queries.
This session is intended for developers and DBAs who want to learn the basics of how the optimizer chooses between an index range or full table scan.
Presented by: Chris Saxon, Oracle
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Published: 24.02.2017 - This document is restricted to members
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