Sangam18

“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 their packets. 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 who want to learn the basics of how the optimizer chooses between an index range or full table scan and how to make their SQL run quickly!