To answer this question, we need to understand the concept of referential integrity.
Referential integrity is a database constraint that ensures the relationships between tables are maintained correctly. It ensures that foreign key values in a table match primary key values in another table, or are null.
Let's go through each option to understand why it does or does not help to maintain referential integrity:
Option A) Unique constraints - This option is incorrect because unique constraints help to maintain referential integrity. They ensure that no two rows in a table have the same values in the specified columns.
Option B) Primary keys - This option is correct because primary keys help to maintain referential integrity. They uniquely identify each record in a table and are used as foreign keys in other tables to establish relationships.
Option C) Cascading actions - This option is incorrect because cascading actions help to maintain referential integrity. They define what happens to related records in other tables when the referenced record is updated or deleted.
Option D) Foreign keys - This option is incorrect because foreign keys help to maintain referential integrity. They establish relationships between tables by referencing the primary key of another table.
Based on the explanations above, the correct answer is A) Unique constraints. Unique constraints do not directly help to maintain referential integrity; instead, they ensure that no duplicate values are present in specified columns.