CS 4432lecture #11 - indexing & hashing1 CS4432: Database Systems II Lecture #11 Professor Elke A. Rundensteiner

CS 4432lecture #11 - indexing & hashing2 Index definition in SQL Create index name on rel (attr) Drop INDEX name

CS 4432lecture #11 - indexing & hashing3 CANNOT SPECIFY TYPE OF INDEX (e.g. B-tree, Hashing, …) OR PARAMETERS (e.g. Load Factor, Size of Hash,...)... at least in SQL... Note

CS 4432lecture #11 - indexing & hashing4 ATTRIBUTE LIST  MULTIKEY INDEX e.g., CREATE INDEX foo ON R(A,B,C) Note

CS 4432lecture #11 - indexing & hashing5 Motivation: Find records where DEPT = “Toy” AND SAL > 50k Multi-key Index

CS 4432lecture #11 - indexing & hashing6 Strategy I: Use one index, say Dept. Get all Dept = “Toy” records and check their salary I1I1

CS 4432lecture #11 - indexing & hashing7 Use 2 Indexes; Manipulate Pointers ToySal > 50k Strategy II:

CS 4432lecture #11 - indexing & hashing8 Multiple Key Index One idea: Strategy III: I1I1 I2I2 I3I3

CS 4432lecture #11 - indexing & hashing9 Example Record Dept Index Salary Index Name=Joe DEPT=Sales SAL=15k Art Sales Toy 10k 15k 17k 21k 12k 15k 19k

CS 4432lecture #11 - indexing & hashing10 For which queries is this index good? Find RECs Dept = “Sales” SAL=20k Find RECs Dept = “Sales” SAL > 20k Find RECs Dept = “Sales” Find RECs SAL = 20k