Referential integrity nuance — evaluate the claim: “When a foreign-key column exists without an explicit FOREIGN KEY constraint, a ‘casual relationship’ between the two tables has been created.” Choose whether this is correct or incorrect.

Introduction / Context: Foreign keys enforce referential integrity (RI) by constraining values in the child table to those existing in the parent. The statement suggests that merely having a column intended to reference another table creates a “casual relationship” without a formal constraint. This probes understanding of logical design versus enforced integrity.

Given Data / Assumptions:

• A column named, for example, customer_id exists in an orders table.
• No FOREIGN KEY constraint has been defined.
• Application code may still treat the column as a reference by convention.

Concept / Approach: Without an explicit FOREIGN KEY constraint, the database engine will not enforce RI. The link is at best conventional or “soft,” relying on application discipline. Such conventions are brittle: orphan rows can appear, deletes in the parent can leave dangling references, and updates may violate intended links. Therefore, the statement that a relationship has been “created” is incorrect; only a column has been created. A relationship, in the relational sense, requires an enforced constraint or a join condition used in queries—preferably both.

Step-by-Step Solution:

Verification / Alternative check: Attempt to insert a child row with a non-existent parent key; without the constraint, the DBMS accepts it, proving the “relationship” is not enforced.

Why Other Options Are Wrong:

• Matching names or isolation levels do not create constraints.
• “Indeterminate” is wrong—behavior is clear and testable.

Common Pitfalls: Relying on naming conventions instead of constraints; believing ORMs automatically enforce RI at the server without explicit DDL.

Final Answer: Incorrect