Placing a not null constraint on a column requires that the data in the column must contain a value, and cannot be null. This prevents users from adding a "blank" value. A not null constraint cannot be added if the column already contains null values.
Notes:
•A not null constraint can replace a "Require a value" rule. R:BASE does not build an index for a not null constraint, but since it stores the not null as part of the column definition, it is able to check the constraint faster than it could check the rule.
•If null values already exist, the values must first be edited to actual data values, before the not null constraint can be added.
