Detailed explanation and options for the selected question.
What is the purpose of the PRIMARY KEY constraint in a table?
A.
To uniquely identify each row
B.
To allow duplicate values in a column
C.
To ensure all rows are NULL
D.
To create a relationship with another table
Explanation:
The PRIMARY KEY uniquely identifies each row in a table and cannot contain NULL or duplicate values. Option B allows duplicates, Option C implies NULLs, and Option D describes foreign keys.