Chapter 1-3: Data Dictionary

File Keys

For each indexed file, you specify a primary key and up to 16 alternate keys. A primary key is required for each file, while alternate keys are optional.

A primary keyprovides the default key path by which to access and retrieve specific records in an indexed file. Unless otherwise specified by a user or designer, the primary key path is always used. The field you designate as the primary key should generally be short and must be unique. A primary key is often used as a link to data in other files. Examples of primary keys include a customer number in a customer file or a product code in a product file. Appx Date/Time fields normally cannot be used as a primary key since the speed of computers would most likely create multiple records within a hundreth of a second, the smallest level of precision for a date/time field.

Alternate keys provide optional key paths by which to access and retrieve specific records in an indexed file. A user or designer may optionally choose to change from the primary key path to any alternate key path for record access and retrieval. Examples of alternate keys to a customer file might include customer name or phone number.

APPX allows you to have duplicate alternate key values in a file, although a unique primary key is required. For each key path, you specify whether duplicate key values are allowed.

When you define a field to be the key to your file, there are two fields in the Key Control pop-up box in addition to Key Type:

Key/Field Order can be defined as ASCENDING or DESCENDING. The default is ASCENDING.

User Selectable? determines whether or not a user can switch to a key path with the Select Access Path option from within an input process. The default is 'yes' .

A field does not have to be designated as a key to be used as a sort field in query processes. During sorting, APPX can use any fields to generate the required sort order.

A File Key Field cannot contain an occurrence specification. This is true for both a single field or a field defined within a Group.

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