Question: 3
(Choose 1 answer)
Choose the correct statement about the impact of declaring a key for a relation R using PRIMARY KEY or
UNIQUE:
A. PRIMARY KEY: does not allow NULL values. UNIQUE: allows NULL values.
B. PRIMARY KEY: allows NULL values. UNIQUE: does not allow NULL values.
C. PRIMARY KEY: does not allow NULL values. UNIQUE: does not allow NULL values.
D. PRIMARY KEY: allows NULL values. UNIQUE: allows NULL values.
