Which statement about a primary key in a relational database is correct?

Which statement about a primary key in a relational database is correct?

• A. It must contain only numeric data
• B. It is always the same as the foreign key
• C. It can have duplicate values
• D. It uniquely identifies each row in the table

Answer: (D)

A primary key uniquely identifies each row in a table. Because of that, its values must be unique and non-null, and the key can be a single column or a combination of columns (a composite primary key). It doesn’t have to be numeric; any data type can serve as a primary key if it guarantees uniqueness. A foreign key, by contrast, references the primary key of another table to maintain relationships, but it is not required to be the same as the primary key of its own table. Since duplicates are not allowed in a primary key, and it must identify rows distinctly, the statement that it uniquely identifies each row is correct.

A primary key uniquely identifies each row in a table. Because of that, its values must be unique and non-null, and the key can be a single column or a combination of columns (a composite primary key). It doesn’t have to be numeric; any data type can serve as a primary key if it guarantees uniqueness. A foreign key, by contrast, references the primary key of another table to maintain relationships, but it is not required to be the same as the primary key of its own table. Since duplicates are not allowed in a primary key, and it must identify rows distinctly, the statement that it uniquely identifies each row is correct.