Table A

Table B

47

ABC

17

QRS

85

FCP

81

MLI

93

CJP

87

DJS

19

KMP

View A

View AB

CREATE VIEW A

CREATE VIEW AB

AS SELECT ...

AS SELECT ...

FROM TABLE A 

FROM TABLE A, TABLE B 

WHERE ...

WHERE ...

Figure 1 7   Relationship between tables and views

Indexes

An index is a set of keys, each pointing to rows in a table. For example, 

table A has an index based on the first column in the table (Figure 1 8). This 

key value provides a pointer to the rows in the table: value 

19

 points to record 

KMP

. An index allows efficient access when selecting a subset of rows in a 

table by creating a direct path to the data through pointers.

The DB2 SQL Optimizer chooses the most efficient way to access data in 

tables. The optimizer takes indexes into consideration when determining the 

fastest access path.

 Chapter 1. Introduction 

15