Which key helps enforce identity and integrity in a table?

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Question: Which key helps enforce identity and integrity in a table? 
Options: Composite key, Primary key, Foreign key, Candidate key

Option 1 — Composite key: A composite key is formed by more than one column and can be used to enforce a uniqueness constraint across those columns. While it helps identify a row when a single column isn’t unique, it does not by itself universally establish the primary identity of a row in the table. It’s a mechanism for a compound identifier, but not the standard means of enforcing entity integrity alone.

Option 2 — Primary key: The primary key is the canonical identifier for each row in a table. It enforces entity identity by guaranteeing uniqueness and not allowing null values, thereby maintaining the table’s identity and integrity as the main unique reference for records.

Option 3 — Foreign key: A foreign key establishes a link to a primary (or candidate) key in another table and enforces referential integrity between tables. It ensures that references across tables are valid, but it does not directly enforce the identity of rows within the table itself.

Option 4 — Candidate key: Candidate keys are attributes (or sets of attributes) that could serve as a primary key because they could uniquely identify a row. They represent potential keys, not necessarily the actual enforcing mechanism unless one is chosen as the primary key. They contribute to the design of identity, but alone they do not enforce identity and integrity in the same authoritative way as a designated primary key.

In summary, while composite and candidate keys relate to unique identification, and foreign keys govern relationships, the primary key is the standard mechanism that enforces the table’s identity and overall integrity by ensuring each row is uniquely identifiable and non-null. The essential distinction is that the primary key is the dedicated, enforced identifier for records within the table, whereas the others serve related but separate roles.

Which key helps enforce identity and integrity in a table?

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