Kbase 12196: Unknown or null value representation Mandatory and initial
| Autor |
Progress Software Corporation - Progress |
| Acesso |
Público |
| Publicação |
10/05/1998 |
|
Unknown or null value representation Mandatory and initial
PROGRESS stores the unknown, or null, value in the database with the
hexadecimal representation of 0xfd.
The unknown value is truly "unknown" in terms of the data value of a
field. There are two side-effects of this issue:
* Logicals may have one of three, not two, values. A logical may
be TRUE, FALSE, or UNKNOWN.
* If a field is a component in a unique index and you design the
application to allow the UNKNOWN value in that field, you can
create and save data records with seemingly duplicate keys. The
records are neither unique nor duplicate because PROGRESS doesn't
yet know the value for the field.
To prevent this side-effect from happening, follow these steps.
1) Make the field MANDATORY in the Dictionary definition.
2) Place a question mark (?) in the initial value field of the
Dictionary to make the initial value UNKNOWN.
Progress Software Technical Support Note # 12196