Which column property in a relational table specifies whether cells must contain a value (that is, whether blanks are allowed)?

Introduction / Context:
Every column definition includes properties that control the kind of data permitted and whether data is required. Knowing where “must have a value” is configured is fundamental to schema design.

Given Data / Assumptions:

• The question asks which property enforces “value required.”
• We are not selecting the data type or a default value.

Concept / Approach:
Nullability (null status) controls whether NULLs are permitted. Declaring a column NOT NULL ensures every row must supply a value. This is different from data type (which sets format/precision) and default value (which supplies a value if one is omitted).

Step-by-Step Solution:

Verification / Alternative check:
DDL examples: column_name data_type NOT NULL; enforced by the DBMS on INSERT/UPDATE.

Why Other Options Are Wrong:
Data type: Defines form, not presence.
Default value: Supplies a value, but does not itself forbid NULL unless combined with NOT NULL.
Data constraints: A broader category; nullability is specifically the null status.

Common Pitfalls:
Assuming a default value implies NOT NULL; it does not. You can still insert NULL unless NOT NULL is specified.

Final Answer:
Null status