Progress/400
Product Guide


Progress Unknown Value Support

Progress/400 uses SQL NULL support to provide the Progress unknown value. The DB2/400 field must allow nulls to support this feature.

When you create a field using the Progress/400 Data Dictionary, you can select Null Capable, which allows the field to have no initial value. If you assign a question mark (?) in the Initial Value field of the field Property sheet, no initial value is assigned. If you want to assign a value to a NULL capable field, use the ASSIGN or UPDATE statements and enter data.

Follow these steps to select the NULL Capable option for a field:

  1. Choose the Field mode button in the Progress/400 Data Dictionary main window.
  2. Choose Modify Schema.
  3. Select the table that will contain the new field from the Tables list.
  4. Choose the Create Field button. The following dialog box appears:
  5. You can select the Mandatory or the Null Capable option setting. Table 2–4 displays possible settings for these two values. This table also describes which assignments are allowed based on these option settings.

    Table 2–4: Progress/400 Data Dictionary Options for SQL NULL and Unknown Value Assignments  
    Mandatory
    NULL Capable
    Result
    ON
    ON
    4GL prevents (?) assignment for unknown value.
    OFF
    ON
    Any value is legal.
    ON
    OFF
    4GL prevents (?) assignment.
    OFF
    OFF
    Any value is legal.

  6. Enter a question mark (?) in the Initial Value field.
  7. Activate the Null Capable option.
NOTE: If you currently have data files that do not support SQL NULLs and have the legacy unknown value, see "Legacy Support and the Progress Unknown Value."


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