Extended Functions of ASF › Creating Indexes

Creating Indexes

Advantages

The Extended Key Definition screen is used to index a table. Place indexes on a table:

• To have control over the data being stored in a table. By placing a unique key on a table, you prevent duplicate rows from being included in the table.
• To sort the data stored in a table. The rows can be sorted according to the value of a key column, in either ascending or descending order.
• To help ASF process join and selection criteria efficiently.

Types of Indexes

On the Extended Key Definition screen, you can define the following index keys:

• Multiple keys for a table
• Unique or nonunique keys for a table
• Concatenated keys that consist of multiple columns

You can also specify the order in which you want the rows of a table to be stored and displayed.

Keys can be defined for stored tables only. Since data is not actually stored in a view, keys are unnecessary and are not allowed for views. Columns that are defined as work fields cannot be included in an index key.

A sample Extended Key Definition screen is shown below.

                                                    CA
  XKEY   CA - Automatic System Facility          *Extended Key Definition*
  DC560906 ADD/MODIFY KEYS
  Table Name: JOB
                                                   _ PF1 - Help  Page:  1  of  1
  Storage Sequence: 00001  Next/Prior/First/Last/Key Number
  Display Sequence: 00001  Same/Key Number                 Additional Keys
                                         Key Number: 01   02   03   04   05   06
                                  Fast   Duplicates: NO   LAS  LAS  LAS  LAS  LAS
                                 Access  Ascending.: YES  YES  YES  YES  YES  YES
           Column Name            Keys                       Column Order
  JOB NUMBER                       _                  11
  DEPARTMENT                       _                      22
  TITLE                            x3                      
  SALARY                           _                      1
  CURRENT STATUS (FILLED OR OPEN)  x

1. A unique key
2. A concatenated key consisting of two columns
3. Individual non-unique keys

The Extended Key Definition screen is used to specify the following:

• Fast access keys
• Additional index keys
• Storage and display sequence for data

Each of these topics is discussed separately below.