ILE COBOL Programmer's Guide
If a field is null-capable and used in a check constraint, then depending
on the field's value, the constraint may, or may not be, affected:
- If a field (column) value in a record (row) is not null, then
the field is used in the validation process of the check constraint to return
either a status of valid or check pending.
- If the field (column) is null, then the field (column) value is
not used to validate the constraint, unless the check constraint
specifically tests for a null value. This means that the affect a null
field will have on a check constraint is unknown.
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