# Question 2. Please select the correct statement(s) regarding keys in relational models. A. A candidate key is a key (super key) with a minimal set of attributes (cannot remove any attributes from this set, and the remaining one(s) still satisfy the key constraint). B. A candidate key is another term for key (super key) in relational models, and they have exactly the same meaning. C. One of the candidate key(s) is selected to be the primary key, and other candidate keys can be declared as UNIQUE. D. We can select multiple candidate keys to be multiple primary keys for a relation (multiple primary keys, not a primary key with multiple attributes). E. The attribute in a primary key does not accept NULL.
# Question 2. Please select the correct statement(s) regarding keys in relational models.
A. A candidate key is a key (super key) with a minimal set of attributes (cannot remove any attributes from this set, and the remaining one(s) still satisfy the key constraint).
B. A candidate key is another term for key (super key) in relational models, and they have exactly the same meaning.
C. One of the candidate key(s) is selected to be the primary key, and other candidate keys can be declared as UNIQUE.
D. We can select multiple candidate keys to be multiple primary keys for a relation (multiple primary keys, not a primary key with multiple attributes).
E. The attribute in a primary key does not accept NULL.
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