Relational requirements: Which of the following is NOT a restriction for a table to qualify as a relation under the relational model?

Introduction / Context:
Relations have formal properties that distinguish them from arbitrary tables. These properties underpin set-based reasoning and eliminate ambiguity in queries.

Given Data / Assumptions:

• Using classical relational model assumptions.
• Atomicity of cells (1NF) is required.
• Row uniqueness is a requirement for a relation.
• Attributes have names and defined domains.

Concept / Approach:
In the relational model, tuples are unordered and attributes are a set, not an ordered list. While SQL interfaces may display columns in an order, the model does not require any column ordering. Atomic values, uniform domains per attribute, unique rows, and unique attribute names are expected.

Step-by-Step Solution:

Verification / Alternative check:
Relational algebra treats relations as sets of tuples over a set of attributes; sets are unordered.

Why Other Options Are Wrong:
They each state valid relational restrictions (atomicity, domain consistency, row uniqueness, unique attribute names).

Common Pitfalls:
Assuming the presentation order in a UI reflects a theoretical requirement; it does not.

Final Answer:
The columns must be ordered.